SCPOP use the Roland Sound Canvas (an external hardware module) to produce the sounds. Hauptwerk does everything entirely in software, so it only requires a sound (or audio) card.

It largely doesn't matter what sound card you have except for the quality of the D-A converter and the latency. The XG should sound fine.

I believe that you wont need to (or be able to) play it through the SC88 because that can't output sound directly from software programs - it uses its own sounds. SCPOP just controls the SC88, where the sounds are stored and produced.

Hauptwerk's samples were recorded from a real pipe organ; one large sample for every pipe, hence the results are very realistic.

Your MIDI set-up sounds ideal. All you need to be able to do is connect the MIDI output from both keyboards and the pedalboard into the computer. If you can already do this (presumably you can for SCPOP), then Hauptwerk should work fine with your current wiring. A MIDI merge box is just a means by which you can join several MIDI ouptuts to a single MIDI input on the computer.

Let me know if you have problems downloading the program. The website seems to be fine at the moment.

Thanks,
Martin Dyde.