maybe a stupid question but I'm not too well versed in MIDI yet. I currently have my Kross 2 and FA-08 connected to my Mac through USB. Suppose I get the VR-730 (which doesn't come with that many sounds) : can I connect the VR-730 to my FA-08 with MIDI and use the FA-08 sounds on the VR-730, and at the same time, still have access to those sounds on my FA-08 (same question goes for the Numa, really).
Not a stupid question at all, especially since even though the concepts are constant, the particulars vary with every board combination. In fact, it's really a multi-part question...
1. Can you drive FA08 sounds from an external board, while continuing to independently play the FA itself (whether with the same sounds or with other sounds)?
Yes. You can do this with a direct connection to its MIDI jack. Unknown to me is whether you can simultaneously have your FA-08 and Kross communicating via your computer using their USB connections while also using the FA's MIDI connection for direct connection to another board. Some boards lets you use their USB and MIDI ports at the same time, others require you to go into a menu and choose one or the other, and I'm not sure which category the FA falls into. (You could presumably also connect all three keyboards to your Mac over USB and use software to route MIDI from one to the other as desired, I've never done anything like that.)
2. Can the VR-730 and/or Numa Compact 2X trigger sounds from another board (in this case, the FA)?
Yes. VR730 has 100 Registrations, Numa Compact has 99 User Programs. In either case, this is where you can save your choices as to which MIDI channel or pair of channels you want to transmit on, over which set of keys. Meaning that either of these lets you play up to two FA-08 sounds at a time from its keys (split or layered). VR730 lets you send out a single MIDI Program Change on any channel, Numa lets you send two Program Changes, one on each of the transmission channels you specified. I point that out because the first approach would be more useful for using the second keyboard to change Studio Sets on the FA, the second approach would be more useful for using the second keyboard to change individual FA sounds
without changing the Studio Set (leaving the other sounds you're playing from the FA's own keys unchanged). You could still do the latter on the VR, but only for one sound rather than for two split/layered sounds. At least this is how I understand it, never having done it myself. There are numerous other differences in their MIDI implementations, but the bottom line is that either should let you do what you want.
VR730 vs NC2X is an interesting comparison, I'm not sure of all the differences, but here are some advantages I think each has over the other:
NC2X
* aftertouch
* built-in speakers
* sliders that send MIDI CC (making them more useful for controlling sounds in another device)
* allows you to apply effects independently to your two split or layered sounds.
* user programs respond to MIDI Program Change (so you can easily select its sounds via another keyboard, iPhone, etc.)
* supposedly you'll be able to load in your own user samples, but the software to do that has not been made available yet
VR730
* more built-in sounds
* drums
* looper
* more editable parameters for the synth (using iPad)
* better sounding organ (IMO at least)