Okay, we can see what you are not understanding, hope we can explain it.

For example, when I turn on my MX61, the first two of the 1-16 button voice settings are as follows:

Not exactly true, but we understand that is what you are seeing.

When you turn on your MX61 your screen may be showing the VOICES in PART 1 and PART 2. Which one or if both are sounding will depend on whether you are playing SINGLE, LAYER or SPLIT. When only a single VOICE is sounding you will see the keyboard icon flashing in response to Note-On events on the right side of the screen next to the VOICE that is sounding.

When you press button [2] you are simply changing the VOICE assigned to PART 1 from "ConcertGrnd" (the first Voice in the Piano Category) to "Vintage'74" (the first Voice in the KB or Keyboard Category. You are simply changing the VOICE assigned to PART 1.

The "Syn Strs 1" is assigned to PART 2, (of PERFORMANCE 001) if the little keyboard icon to right of the screen is not indicating activity, this PART can be considered "in waiting"... this means in order to activate it you will need to press either the [LAYER] button (which will map the Syn Strs1 across the entire keyboard) or you press [SPLIT] which will map the Strings to left side of the per stored Split point.

Here's what is happening:
Press the [SELECT] button under the screen. You will now see the NAME of the first Performance. What ever you stored to the first PERFORMANCE location (the AP: 001 ConcertGrand + Str: 078 Syn Strs 1

A PERFORMANCE contains PARTs 1, 2 and 10. Whether PART 2 is active will depend on whether or not you stored the PERFORMANCE with the LAYER or the SPLIT button lit. Whether PART 10 is active will depend on whether or not you've stored the PERFORMANCE with a RHYTHM PART active.....

When the [SELECT] button is lit, you can move to from PERFORMANCE 001(A01) to PERFORMANCE 001(A02) using the [+1/YES] button.

When you [SHIFT] + [A CATEGORY BUTTON], you will move to PERFORMANCE DIRECT SELECT, now the individual buttons can advance through the PERFORMANCES. (Added with update version 1.01)

Not sure how 078 replaced 083 as the start-up Part-2 voice, but I'd actually like to keep it that way when I do a quick reset, if that's possible. Is it?

You have obviously stored a PERFORMANCE in location 001(A01), which is your choice. It will remain there even if you do QUICK RESET - remember the QUICK RESET is an EDIT BUFFER - it does not really overwrite anything UNTIL you press [STORE]!!!

You can keep whatever PERFORMANCE you want in PERFORMANCE 001, but the [SHIFT] + [SELECT] Quick Reset routine is the factory default to build your own PERFORMANCE - you can store your new Performance in any of the 128 locations 001(A01) through 128(H16)

Hope that helps.

Helps indeed; I've got a clearer picture now as to how it works -- thanks!

Incidentally, the PERFORMANCE DIRECT SELECT v1.01 enhancement is a major plus (for me) on this kb.