That might be the 8580 Sid replacing the 6581 (not sure about the numbers). I never heard the 6581 in original, but as far as i know there is not much of a difference. I red that 8580 has less noise while some people say the filters of the 6581 sound better and also it sounds more dirty.
There is a big difference when using with MSSIAH. (And when playing back SIDs! When they're composed specifically for one or the other.)
The Bassline, Monosynth, and Drum portions of MSSIAH are said to be designed for use with the 8580.
I have used MSSIAH on both versions of SID and can say that the authors are right when they state in the manual that there is a big difference in sound, when an instrument or module is designed for one specific chip. The filters on the 8580 let some sound through that the filters on the 6581 would just totally cut off, IIRC.
It really depends what you're after... the original 6581 is more what we remember from video games, and the 8580 has greater refinement for sound synthesis.
I have started messing around with the MSSIAH's Sequencer and can say that it really is truly exceptional, and that people just using MSSIAH as a soundbank are missing out. If you want to use MSSIAH with Octamed, definitely just take MIDI Out from Octamed to the MIDI In (there's only one!) on the MSSIAH. Have Octamed send MIDI Clock, and then turn MIDI Clock *on* in MSSIAH sequencer. Then whenever you "start" Octamed, MSSIAH should start along with it, and play back in sync. You can loop any portion of your MSSIAH sequence, edit it as it's playing back, and mute/unmute tracks, all live. This would be a great setup for using sampled sounds via OctaMED and synthesized sounds via MSSIAH. I'm not an OctaMED or OSS user though so YMMV. I have slaved MSSIAH to my drum machine, and also to an Amiga running Bars & Pipes. It's very reliable.
Definitely get a C=1351 mouse as someone else said, or be like me and find a Micromys. MSSIAH supports the scroll wheel on PS/2 mice connected via Micromys.
- t