Howdy, Joker!
I had the pleasure of playing the Tri 208 up at Low Down Sound when I went cab shopping last spring. I walked away from the store with an Epifani T-112 and T-110UL, but that is another story (which you are already familiar with!

). Back to the Tri 208, it really is a fantastic sounding cab. However, it is not quite as efficient (98.1 spl) as the Epi's or the larger Accugroove Mini Whappo (both at about 100 spl), so I didn't think that it would work as well with my Walkabout head. Of course, now that I have an iAMP 800, I may have to rethink the Tri 208.
Tonally, I found it to be very accurate, but fairly laid back. Quite reminiscent of my VL-208's. I would love to A/B them sometime. By comparision, the Mini Whappo and the T-112/T-110UL combo sounded sharper, with a bit more frequency extension on both the low and high end(which is somewhat weird, since the Tri 208 is rated at 35Hz to 18kHz). I'm guessing that the efficiency thing was at work, here. I would think that two Tri 208's would sound great together, but that'd be a 2 ohm load (which your Clarus could handle, of course!).
I would agree that the Tri 208 would be a great upright cab, or a studio recording cab for electric/upright (which is what it was designed to be). For live use, however, I would suggest the Mini Whappo. That little cab is very impressive. Tonally and volume-wise, it was actually quite close to te T-112/T-110UL combo I have raved about. Less coloration, of course, and all in all slightly superior. However, at the time, the additional portability of the two Epi's made a big difference. I am still left with a severe case of Accugroove envy, though!
Then of course, there is the Whappo, Jr. I have been lusting after...
The Accugroove stuff is very well made, very uncolored, and quite flexible for both upright and double bass. I would strongly suggest that you check them out.
Later, Tom.