Thanks, Bcgator, glad to help.
Smhyde, here's the MSRP for the speakers when new,
DM604 S2 - $1600/pr
CC6 S2 - $350/ea
Assuming the speakers function perfectly, IMHO, price would be an absolute maximum of $650 for the DM604 S2's, and $150 for the CC6 S2, and they would need to be in perfect cosmetic condition with original shipping cartons, carpet spikes, and rubber feet. Ideally, somewhat less would be better, and adjust price for any cosmetic issues. If there is a functional issue, or any physical damage to a driver, price should drop dramatically, as parts are expensive, and it would be best to check availability. It may be possible to see prices higher than this on ebay, which is usually due to a bidding war between two potential buyers, and the seller still has fees of 15-20% after the sale.
If you do decide to go for the DM604 S2's, I would also get the CC6 S2. This would keep a match for the front three speakers, and the Nautilus tweeter in the CC6 S2 is definitely better than the tweeter in the CC6.