B&W DM604 S2 worthy upgrade from DM603 ?

@Tls49, that's good info regarding the distribution of content across multichannel, I'm glad you pointed all of that out. Using that info, it sounds like more of a benefit than I thought, in re-purposing the 603 from front to back.

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.

Thanks Bcgator,

The speakers seem to sound find, but one thing I did notice that has me a little nervous about them - there appears to be an ever so slight amount of rust on the bolts that hold the speakers in the cabinet. In my area that could be an indication that they were in a waterfront home and subjected to a salty environment. If it's just a tiny bit of surface rust on those bolts, I suppose I could live with that, but I just wonder if that's a warning sign that I should move on for possible other reasons.

Other than that, they appear to be in good condition. I'm sure there are no boxes. I don't know about the carpet spikes and rubber feet.

I don't recall my DM603s coming with spikes - or maybe I have them in storage and have forgotten about them.

Smhyde,
Tls49 has been very helpful here re. info & pricing. I just wanted to add my 2 cents re. pricing: I bought my DM604S2 back in 2001 brand new from the retail store for less than $800/speaker. They always went for a discount. I.E. the street price for brand new speakers was always less than $1600/pair. I believe I paid something like $1400/pair. Today we are in 2014, 13 years later. if you can help it, I would say that you should pay less than $600/pair today after 13 years & a little bit of rust on the bolts holding the drivers in the cabinet.
Given the info provided by Tls49, I agree that the DM604S2 would be a very nice upgrade for you for (hopefully) not too much money.
Of course, my opinion, FWIW. thanks.

Smhyde, if you determine that the rust is due to a salty environment, keep in mind that the internals of the speaker have been exposed to that same environment because this is a ported speaker. The same would not be true for a sealed cabinet speaker.

Tough call, but if this is due to a salty environment, IMHO, I would probably pass on them, unless you can get them extremely cheap.