There are several things that could be impacting your results. For example, if you select an accurately mapped violin Part in Part 1, it will only appear on notes G2 and above. The acoustic instrument, violin, does not generate any notes below G2 (the “G” below middle C).

Now, some AWM2 violin Parts will have what is referred to as a ‘composite’ Waveform... this is a waveform that is used to *fiil in* the range either above or below the range of the principal instrument being emulated. Some violin Parts are accurate as to violin range.

Additionally, assigning Arp Phrases requires that the phrase is set, or offset, so that it can properly trigger the instrument Part to which you’ve assign it.

What we can tell you without more detailed info follows:
Start by layering the violin and the orchestral marimba. That is turn the [ARP ON/OFF] = Off.
When we hold master classes on programming we always start with LAYERING as this logical.

A SPLIT, is a Layer that has been divided by a Note Range decision. So by Layering, and playing them together you can get an idea of what ranges they each naturally cover. Then set your RANGE for each Part on the HOME screen. You may determine that you need to offset how each Part responds to the Keys you are pressing. You do this by manipulating the Part’s NOTE SHIFT parameter (which allows you to raise or lower the pitch you hear when striking the Keys).

For more definitive info, can you tell us how you went about selecting the violin and the marimba?

And when it comes to using more than one Part and Arpeggiators, you must setup a second Split Point.
The is the Split Point that assigns one sound C-2 thru B2 and the other C3 thru G8 is called the Part Note Limits. This influences what sound is made when you directly press that Key.
You must also setup, separately, the Arp Note Limits. These determine which notes on the keyboard will influence *controlling* the chord intelligence for that Part. You do not want keys in the right hand influencing the Arp assign to the left, and vice versa.

[EDIT] > select Part 1 > tap “Arpeggio” > “Common” > set the Note Limits - these are the notes you want to use to control the Arp’s assigned to Part 1

As you can guess this prevents your right hand from influencing the sound played by the left hand.
Conversely, go to Part 2 and set the Arp Note Limit Range so that just the right hand influences the sound assigned to the right hand.

... so I can do the violin with my left hand and the marimba with my right at the same time

Do you want an arpeggio to play the left-hand violin? Do you want an arpeggio (arp) to play the right-hand marimba? Do you want an arp to play both violin and marimba?

I'm not sure what you are trying to have direct control of where the notes you play are played by the PART (marimba or violin or neither or both) are played verbatim as you strike keys. This would mean no ARP. Or which PARTs you want an arpeggiator to take over to play some "pattern" in response to your trigger note(s).

... if you want the left "half" of the keyboard to do one thing and the right "half" to do something else - and you have arpeggios involved - then you need to be sure to apply a note limit to your arpeggio trigger notes as well. You have both a note limit (range) of the sounding notes ("normal" note limit - which, among other definitions, defines which keys will make sound when the ARP is turned off). And you also have an ARP note limit which defines which notes trigger an ARP. This is under the Arpeggio->Common menu. You would want to set your arpeggio note limit to stay away from the other hand's note limits.

I'm not sure if you're setting the correct menu of note limits to realize the split you're anticipating when using ARPs.

Thank you for your help. I think that the root cause was the note limit setup under arpeggio. I was not aware of this. I added it to my first performance configuration but I must have something else set incorrectly because it did not work. But, I deleted the first performance and set it up again and it worked correctly.

I cannot tell you how impressed that I am with everyone's responses. I have never used such a responsive group who actually provide quality answers. Thank you all.
Glenn