Just did a bit of reading up on this tube, as it came up in the thread on Chris' new HT5, which uses one in the power amp. Turns out it's compatible with a 12AX7/12AU7, and is basically a pre-amp tube, simply with a higher current rating.
I also read that using one in your pre-amp will kill your gain and low-end response, so I doubt I'd use one in my TriAxis, but it might be cool in my Sovtek, which already has oodles of low-end.
From what I've heard, one of the triodes is higher gain than the others. Kind of like half a 12AX7 and half a 12AT7 in one tube. I don't remember exact specifics though.