can rcas and xlr's mix in the same system

The answer is yes, but I would go all balanced , because most , if not all of Classe's products are internally truly balanced.

Actually I re thought your post. I would still go all balanced , but pertaining to your question, set your pre to balanced and make sure the rca outs are still active with another source ie. TV, VCR, Tape, Tuner whatever, you just want to make sure it does not disable the RCA outs.

Thanks Darrylhifi. when you say disable do you mean damage

No when I say disable I mean if your setting your pre to a balanced mode it may {I dont think so, but it may } prevent the sound from coming out of the RCA outs and only have the sound coming out of the XLR pre outs. Thats why I say test it in advance. If you set your pre to balanced , but still have it hooked to the amp with RCA's , then when you play a different source besides your Cd Player you should hear the sound. If you do then your good to go. But I still say go XLR all the way, you have the equipment that will benefit from it.

On my Classe SSP75, the RCAs and XLRs are all always enabled. I run the power amp out of the XLRs and the sub via the RCA main outputs.