I just found a very nice pair of C-4's on consignment at my local high end dealer (a Energy dealer).   They sound fantastic - even with my nearly 20 year old Pioneer VSX-502.    Since the 502 is so old, should I upgrade to a new receiver?      Any recommendations?   Denon, HK, Onkyo?     or more high end - Rotel, NAD, Adcom etc....    What will mesh well with the C-4's?  (and better yet - what should I avoid?)

 (of course at the dealer they sounded unbelievable (for the price) with Rotel separates.   They compared very well to PMC and JMLabs that were several times more expensive).
 

I'm very glad about the C series

depend of your taste, and your budget

try it with a nad 320 bee  (400$ integrated) more torque more round especially at low volume level more mellow sound

or a cambridge audio 540A (500$ integrated) more clean more dynamics a bit less torque at low volumes but more clean high notes

it will be almost the same sound quality than the rotel separates for the half of the price

rotel sounds much better with more colored in lows speakers it will be a bit harsh with energy but a very good match if you are a percussions listenner

if you're a serious jazz,blues listenner go with nad or bryston(good choice the bryston but more expensive)

but if your a classical,opera casual listenner cambridge,denon,marantz will be a good choice

personnally i prefer uk enginnering for amps than japanese but is a question of taste