Yes, you need two Sids for stereo, but if you've got one brown C64 and one grey 'breadbox' C64, you've got two different versions of the Sid chip, a 6581 and an 8580. Whichever you choose to go with, they will need to match. the minimal requirements are listed about 3/4 of the way down the page here: http://www.ucapps.de/midibox_sid_manual_hw.html for stereo you'd need two sid kits, a core, and a din module from Smash's shop. An LCD would be a good idea as well.