here someone mentioned that the sc-55 sounds better than the sc-55mkii and later because these units allegedly switched to a powerpc-based softsynth: http://nfggames.com/forum2/index.php?topic=5905.0
is there any truth to this?
There is a fair amount of misinformation in that thread, not the least of which is this amazing "soft-synth" notion.
The SC-55 is based on Roland's "GP" synth architecture, and uses a Toshiba-produced, TC24SC201AF custom PCM core. The SC-55mkII uses the (also Toshiba-produced) TC6116AF core, which is better-described in the JV-880 service notes as being a TC24SC201AF with integrated HG62E11B23FS gate array. Given the much-improved output stage of the SC-55mkII, it's my opinion that anyone suggesting that the SC-55 is the better-sounding of the two hasn't done an adequate comparison. The difference in clarity and soundstage is strikingly obvious to me.
Roland's follow-up "XP" synth architecture is based around the Fujitsu-produced, MBCS30109 custom PCM core, and is found in the SC-88, JV-1080, XP-variants, etc.
Concerning CPUs, the SC-55 and SC-55mkII use a 16-bit Hitachi H8/532, and the SC-88 uses a 16-bit Hitachi H8/510. It's the JV-1080 and XP-variants that use Hitachi's 32-bit SH7034, SuperH RISC Engine.
[Edit: Corrected my own misinformation]