Of course this is speculating: this is what we are doing here all the time.
Hi Kari --
Thanks for the post. It's nice to hear from someone who is interested in the circuit level.
I've crawled through the schematics of the Montage and and the Yamaha patents covering the memory interface, etc. for the tone generator.
http://sandsoftwaresound.net/montage-hardware-platform/ and
http://sandsoftwaresound.net/swp70-tone-generator/So, yeah, I'm already familiar with ONFI.
There are two very different purposes for the internal drive (maybe it's an SSD, maybe not) and the waveform memory. The waveform memory directly feeds the SWP70 through a dedicated communication bus, ONFI compatible. The TG actually gets its incredible memory bandwidth through its dedicated wave working memory (SDRAM) which better supports random access than NAND flash.
The internal drive holds styles, MIDI song files, etc. and communicates with the host (control) computer (i.e., an ARM processor in the Montage, who knows what in the Genos.)
Yamaha has used (roughly) this architecture in every high-end Motif/Montage synth and every Tyros.
Of course, we're all welcome to design our own synthesizers.
I'm just holding back my own speculation on what's inside Genos until I can see the Genos service manual.
Hope this helps our discussion -- pj