We have the same speaker/sub combo and my mono's are being upgraded to extreme status. I thought that once I went to the extreme's and high passed them for use with the subs, that I would be in heaven. Lurking in the back of mind was the thought of bi-amping with some tube amps up top.
Now I read that you are having success with this. This is something that I would love to try down the road, as my wife has banned any more expenditures. Tweaks and cables I can hide, but a pair of tube amps would be a little tough.
Me: "They're...uhhh...heaters...yeah that's it, space heaters." 
Spouse: "We live in Florida and winter is over. Try again." 
Can you elaborate a little more on the benefits you are experiencing with this setup over just using the Extremes? You mentioned an all-out assault. I like the sound of that. You also mentioned the smooth sweet sound of tubes. How much different is it than just the Extremes by themselves.
Congrats. I am 
with envy.
Steve
Steve,
Sorry for the delay in replying, we have had out of town guests for the past few days. I'll try to answer your questions.
I think you will be quite happy with the Xtreme's and your Vandy's. The 3A's, IMO, demand good amplification to deliver what they are capable of. The first thing that struck me about the Xtreme's was the dynamics. I powered the 3A's using a stereo Stratos with cap upgrade for about a year but really had the desire to try tubes. A few words about how I arrived here..
I undertook a project to build a pair of 100wpc tube amps using a design from Bruce Rozenblit's "Audio Reality". I chose this design because I liked the simplicity and inherent balance of only two output tubes and because I was quite happy with my Grounded Grid preamp. Once I had the new amps up and running, debugged and broken in, it didn't take long before the Stratos ended up stored in another room. The bass was not as good, as expected but the midrange and treble had less grain, better low level detail and much better imaging. The sound was just completely removed from the speakers.
I didn't know what to do with the Stratos since I was quite happy with the tube amps. Then in November Klaus announced the Xtreme upgrades and since the amp was gathering dust anyhow I thought I would give them a try and if I wasn't happy, I knew selling them wouldn't be a big deal. In addition I was beginning to miss the tight bottom end. Of course I was hi-passing the amps at 80Hz and these amps have a fairly low (for a tube amp) output impedance, but the bass was still too wooly.
I received my Xtreme's back from Klaus in mid January but unfortunately, one of them had some problems. The upgraded amp was fine but the new amp was DOA on arrival. A bit of looking turned up a loose power transformer primary lead. Very likely a combination of not quite enough solder and UPS rough handling. It was in a very difficult location and tough to solder. I re soldered the lead and the amp fired right up and I thought all was well. Sadly the amp died about 5 days later. A horrifying noise issued from the speaker and it blew two output fuses. I tried replacing the fuses but they blew instantaneously. A call to Klaus and the amp was on it's way back to Indiana. They turned it around quickly and I had it back within 2 weeks. Klaus called on a Sunday to let me know they were working on it and what the problem was. It had two shorted output transistors. No idea how or why but Odyssey repaired it and shipped it back quickly. As usual, Klaus is dedicated to customer service.
Of course I got start break in over again. Now that the amps have settled in, at least for the most part, they are sounding quite good. I haven't posted any kind of review yet, mostly because the ones that are out there reflect the nature of these beasts and I'm sure they are still not quite broken in yet.
The tube amps still deliver a better image/soundstage than the Odyssey's. Not that the Extreme's are bad, it's just the other amps have a spatial quality that is amazing. Some recordings sound like the stage is 30 feet deep, instruments and voices are just "there" and very free of the speakers. The treble is slightly rolled off with the tube amps but that is easily addressed with the control on the speakers. I have them set at +1dB and it sounds very good (to me).
Now that I have the biamp setup working well, I am getting very nearly the best of both worlds. I have exceptionally tight and powerful bass with seemingly unlimited power. I know it's not, but there is no sign of strain at any level I care to listen to. IMO the Stratos amps have not had a big enough power supply, the Exteme upgrade addresses that issue. The midrange and treble is very smooth with the Extreme's, much better than the stereo Stratos, but still not as pleasing as the tube amps. I suspect my tube amps are editorializing a bit, like most tube gear, but I really enjoy the sound. I still get the great spatial imaging and the speakers just disappear from the room.
As a side note, I received a set of NOS Mullard CV4003 tubes over the weekend and they have raised the performance of the preamp up a notch and for kicks I connected the mid/tweeters back to the Odyssey's. Very nice indeed. I could easily live with this configuration and I'm sure it will improve as the Extreme's continue to break in. When playing vinyl I notice less of an SS sound from the Odyssey's than when listening to CD. I suspect the SS grain I do hear is mostly digital grunge being amplified cleanly by the Stratos Extreme's and not the amps themeselves. They seem to be doing a good job of passing through what they are fed. That said, I do like the slightly softer sound of the tube amps when listening to digital, which I do most of the time.
Sorry if I rambled too much.
HTH.
Mike
