I'll bite. Though I've no direct experience with the DC-5 (can't compare, as you asked), I definitely have a long-term (~13 years) relationship with the Triaxis, and I currently power it with a 20/20 - down-sized from 2:90 about five years ago.
First, don't worry about volume: the 20/20 has plenty of oomph in its sleek little soul - enough for clubs unmiked. You'll notice some differences between the DC's 6L6GC power and the 20/20's EL84 power: more upper-mids and less low-frequency impact as you move to the 20/20. This can be an advantage, depending on your style and context (leaves more room for the bass player, for instance). Another advantage of the 20/20 is the capacity to now play with stereo effects; I couldn't live without stereo, and I highly recommend getting two cabinets, if you're making this change, and checking it out. [By the way, are you talking about the vertical 2x12 Recto cab? I've always wanted to try those, but I'm very happy with my dual wide-body 1x12's, especially after the upgrade to WeberVST Blue Dog and Silver Bell alnico speakers].
You can get an amazing variety of tones out of the Triaxis-20/20 setup. And if you care to sprinkle some sonic MSG on your signal, try optimizing your rig with NOS tubes like I have:
( http://www.grailtone.com/forum/viewtopic.php?t=749 ).
Finally, as an inveterate tweaker (I channel my OCD perfectionism this way), I have to comment on the ergonomics of the Triaxis, and rack setups in general. Basically, they
suck.
You're looking at little screens, poking all these buttons, remembering how to carry out non-intuitive protocols. Not the spirit of rock and roll at all, and definitely a different feel than rotating knobs. But you already have a M/B amp, and therefore must be comfortable with perpetual tweakage. The positive side of this, with the Triaxis, is that you can dial it in, save as a preset, and come back to it later without having to redial. Ultimately a time-saver. I hope you have a midi controller so you can take full advantage of this capacity (wait til you try morphing with the continuous controller!).
Hope this helps. What else do you want to know about the Triaxis-20/20?
Cheers!