Upgrade from Quad 11L?

Not sure of your budget for a sub but I used (and still use) a James EMB-1000 with the Quads. This sub has been fairly easy to mate with the various speakers I have owned. Especially after I set it on a 2 inch thick maple block. Very clean bass, musical without the muddy boom boom. Look at my system for a pic of the sub.
Also skeptical that cable swaps will "dramatically" change your sound.
Agree with you on the new Wilco album. haven't listened to it enough to rsnk it among their other albums but it is promising.

Here is a suggestion for isolating your CD player on the same structure as your speakers.

Operating under the assumption that vibration is bad, differentially affects your CD transport and digital components, and that the vibration is coming through the structure of your rack - I would get the largest, hardest and heaviest chunk of hardwood you can find that will fit in your rack under your CDP, a maple chopping block is a good place to start. Place your CDP directly on the block and place the block on several Black Hole sorbothane dots (http://www.tweakshop.com/BlackHolePods.html) between it and your rack. This will isolate your CD player from the rack, give it some extra mass to both resist external vibration and a place for its internally generated vibration to dissipate.

A place to start that has worked very well for me in a rack system that is far from ideal and placed by necessity closer to my speakers than I find ideal. You can experiment with isolating your amp as well using vibrapods or Herbie's footers, but I find my solid state CD player is much more sensitive to vibration than my solid state amp. Tube amps may be a different story...

Thanks for the isolation ideas, Knownothing. I'll start with the cdp.

The James sub is out of my range right now, Timrhu. But it sounds like people have gotten good results adding a sub to the Quads, and there seem to be good options in the $600-750 range (HSU, SVS, REL, maybe Martin Logan Dynamo? and the Aperion 8 is much cheaper). A question for another thread ...

The more I listen to it, the more I like the new Wilco. "Sky Blue Sky" grew on me in the same way (I went from thinking it was nothing special to loving it), and I think this one's even better.

With only a single preamp/sub out on the MH a25.2, it looks like I am limited to Rel (as Bob suggested). Of course I only figured this out when a sub started looking like a good idea ...