Well, to get that typical C64 Sound, you can use an other Option too:
A Tracker for the C64 as a .d64 file and a C64 Emulator. I don't know much about that, startet only Huelsbecks Soundmonitor a few Times and listened to the Demo Song/s, etc. - and i don't know, how to create a .sid file from that, what you create e. g. in Soundmonitor on the C64.
For the Amiga Part: same thing here: Get Soundtracker, Protracker or whatever Tracker you like and a Copy of (Win)UAE and the Kickstart File/s from Cloanto or a Real Amiga 500. And don't forget the rom.key file.