What would you upgrade next?

biggest improvement for you you right off the bat, given my experiences with hearing the vast majority of audio enthusiest's and even audiophile's systems I've come across out there, IS DEFINITELY THE SET UP/ACOUSTICS!!! 50-60%+ of the overall sound you are getting(or not getting) is from proper speaker/seating set up and acoustic considerations in the room! Most fail misserably here, and get poor overall sound with even the best gear. If you have this down, where the speakers are ALL giving you even/flat frequency response(rare...trust me) from the seating possitions, all the speakers are in phase with each other, especially the subwoofer(most have way off), and you are properly dealing with the other acoustic issues in your room, you will improve results greater than any equipment changes you could possibly make!...no understatement.
After that, you should strongly consider upgrading that rather beamy, low dynamics center channel, for the better MC1 that Thiel makes. The SCS3 is the weak link with those speakers. Also, make sure you're crossing over your mains(that's right, the CS6's) at 80hz for movies, and letting the sub handle bellow that! Really, full range music speakers can't handle DD/DTS bass on their own, and NEED to be crossed over higher, even though they play full range.
If, like most, you can't get proper set up results on your own(simply measure with a sound level meter, or listen to ONE SPEAKER in mono/summed stereo to see how your speakers really sound), then have someone help you who's skilled enough(like me) to help you do it!
Otherwise, any upgrades, like better powerconditionsers(PSaudio and better), or better cables will only go so far.(but will help, yes).
good luck...if you get the set up and acoustics right, you're most of the way to world class sound...

Lthkeepr makes a very strong and valid point. Treatments are as good as, or better, than many upgrades. Also, agree with upgrading the Monster. Might I suggest an Audio Magic Stealth - money well spent, IMHO.

I'm with Bob--the preamp is likely a big, if not the biggest, weak link in your system. The good news is you can buy a high-end stereo preamp and just plug the front L/R outs from the B&K into any line-level input on the stereo preamp(the Pioneer also goes into the stereo preamp, which is obviously connected to the McCormack). This way for critical 2-channel listening you're only using the stereo preamp, but you can still use the B&K for movies/surround music--best of both worlds.

Also high on my list, although well behind the preamp, would be to mod the Pioneer(talk to someone like Ric Schultz at EVS, Stan Warren, Dan Wright, etc.) that will clean things up quite a bit, and also sending the McCormack to Smcaudio for the Rev. A mod.

If you're happy with your speakers I think these three upgrades would make major improvements, although again I'd definately start with the preamp. For what it's worth and best of luck.

Tim

Keep the Monster, and buy a Preamp dedicated for music that has a HT pass through...I am doing this and just bought a Sonic Frontiers Line 1, and am amazed how much better it is for 2 channel than my Lexicon DC1. Then again, if your a die hard HT guy, and don't listen to a lot of music then forget what i just said and keep what you got and send me the$$$$;)

Thanks to everyone so far for your suggestions.

Vader, I assume your Sunfire suggestion would be for the ATI as I can't imagine it bettering the McCormack.

Bob, I realize that the Reference 30 is not the highest level pre/pro but it seems to get fairly favorable reviews so I am surprised you feel so strongly that it is out of place. I run the Pioneer's 6-channel analog outs through the analog inputs where no processing is performed, only volume control. I assumed this would be a fairly clean signal. Do you think otherwise? Also, see Tim's response as well. Do you think this setup would yield significant improvement?

Lthkeepr, Point well taken on room acoustics. I am finishing my basement and everything is moving downstairs. I will finally be able to position everything in the proper location as well as be able to allow for acoustic treatment. Wives are funny about putting acoustic material in the living room! My local shop has a demo MCS on sale for $1400. I had already considered upgrading but wasn't sure if more improvement would come from other changes. I think I'll bring it home for a demo!

Tim, I also like your idea as it lets me still use the processor and all of it's distance, loudness, and notch filtering for movies. Have you seen the new McCormack 6-channel preamp? I have read about it but didn't know how much improvement this would add. I think this would allow pass-through for all multi-channel formats, not just 2-channel. Would this accomplish the improvement your thinking I need?