1. I layer a piano and string sound, By itself, this sounds great. (Choosing the piano as the main instrument first then strings after)
2. If I, however, select strings first then add piano after the fact, the entire performance sounds "different" not as musical or as desired for my application. It sounds as though something in the background is being affected, possibly some sort of effects is being added. Can this be disabled?

Is it possible to have the same sound no matter what is selected as the first instrument first?

First, let’s clear up the reason for the difference you are hearing... there is nothing to be disabled, nor is there really anything wrong. Once you understand how “merging” Performances work, you will see that it really is on you to build the rest of the second (merged) Instrument... you only merged a portion of its programming. (That’s why it sounds different).

When you call up a Performance it is in its HOME location. A Performance can be made up of multiple Parts. Those Parts share a set of COMMON parameters. Among those “Common” parameters are the Performance Name, an overall Volume, a Reverb Effect, a Variation Effect, a Master Effect, a Master EQ... additionally it has 8 AssignKnobs linked to the Super Knob and 16 Control Sets

The second Performance in its HOME, has a different Performance Name, a different overall Volume, a different Reverb Effect, a different Variation Effect, a different Master Effect, a different Master EQ... additionally it has its own 8 AssignKnobs linked to the Super Knob and 16 Control Sets

Each Part in a Performance is a complete Synthesizer, with its own Part Name, Part Volume, its own 3-band EQ pre-the Inserts, its own dual Insert Effects, its own 2-band EQ post the Inserts... additionally each Part has its own 8 AssignKnobs and each has its own 16 Control Sets

When you start with a Piano (in its HOME location) and “Merge” Strings to it... all the String Part parameters are brought along. But none of the Common parameters are brought along.

The Strings at HOME are set in a huge Concert Hall setting (as the Reverb Type)... when you merge them over to the Piano’s house, you must join the piano in its much smaller Chamber. Since you can only have one set of Performance COMMON parameters... the string orchestra cannot (does not) bring along the Reverb, or any of the upper Common settings. It inherits the Common settings of its new HOME.

This accounts for the sonic difference... the Performance that is at HOME retains its Common settings, the merged Performance, while it brings all of its Part settings does not bring along its previous Home’s Common settings, if it did... you guessed it: the Strings would sound as before but now the Piano would sound different.

Your task... when merging any Performances, is to make them work in the same room. Here’s what I mean... the upper Common parameters that are making the sonic difference here are those that are NOT a part of the instrument; they are the room acoustics. They are settings that surround the instrument. Those settings that recreate the environment in which all the instruments must play and sound together.

The Piano sound in its HOME has the room acoustics designed specifically to make the piano sound good.
The String sound in its Home has the room acoustics designed specifically to make the strings sound good.

Your job now, once you’ve Merge the two, is to rework the room acoustics to support a piano and a String Orchestra.
If you are surprised that there is a difference, you shouldn’t be.

A famous jazz flute player snuck into the Taj Mahal late one night with a tape recorder, and recorded a record... a glorious sound... if that is the HOME setting (Flute In Taj Mahal) when the Flute player comes by your house and sits down to jam with you at your piano, he can bring his instrument, but, alas, he cannot bring along the Taj Mahal.

Your job is create a NEW set of Common parameters that supports both instruments. Yep, you need to program them.

Extra Credit
A good exercise when “sound designing” by merging already completed Performances...When first looking for a merge-able candidate is to touch “FX” at the top center of the screen to take the shortcut to the “Effect Switch” screen... bypass the System Effects... play the sound with and without those Reverb and Variation Effects. Then bypass the Master FX. See how much it is relying on those... this will help you in determining what you need to do to make this sound work when you move it to a new Home.

Your job is to make the combination sound good. The trick to good mixing (sound design) is making your own decisions about the ‘room acoustics’ once you assemble all the instruments in the room. No one can do that for you. As a recording engineer, you learn early that getting each instrument to sound good individually is just the ante in to play, getting them to all work together is the ultimate goal.

Hope that helps.

Bad Mister

Again, thank you for your eloquent explanation.

Very well understood. I have a bit to learn and figuring out to do. I'll work at designing and constructing my performances and apply your suggestion of "stripping" the sounds to a bare minimum to see how best they would fit with each other.

Extra Credit
A good exercise when “sound designing” by merging already completed Performances...When first looking for a merge-able candidate is to touch “FX” at the top center of the screen to take the shortcut to the “Effect Switch” screen... bypass the System Effects... play the sound with and without those Reverb and Variation Effects. Then bypass the Master FX. See how much it is relying on those... this will help you in determining what you need to do to make this sound work when you move it to a new Home.

Your job is to make the combination sound good. The trick to good mixing (sound design) is making your own decisions about the ‘room acoustics’ once you assemble all the instruments in the room. No one can do that for you. As a recording engineer, you learn early that getting each instrument to sound good individually is just the ante in to play, getting them to all work together is the ultimate goal.

Hope that helps.

If you discover the Variation Effect, for example, is critical to what makes the Strings sound appealing, it may be worth going back to the Piano, which may or may not be using the Variation Effect at all... if it isn’t, then you can go ahead and reprogram it. Finding a sound that fits immediately is one way, but realizing you can get really good at reworking the Effects is even better.

It’s a good exercise to dig into those Performances that appeal to you, and take them apart. Have fun! Thanks for question.

I must say that Bad Mister is just badass at explaining things. I have watched his Montage videos on YouTube. Music skills and verbal eloquence in just one single place. Loved the Taj Mahal simile.