when it says 4xsid chips does that mean that i need to buy 4 c64s to get the chips i need?also what is the polyphony on a midibox sid?
Use the search, Luke 
And read at least a few topics in the forum before asking things that were answered only a few days ago:
http://www.midibox.org/forum/index.php?topic=8691.0
Seppoman
the sid is the soundchip of the c64. and yes … pull it out if it :) You dont need all the 4 for the beginning. 1 SID has 1 mono output. The others are more :). With 4 Sids you would have 4 seperate configurable outputs.