I'd love to get my hands on one of those Palmers! How do you like it so far?
Here's how I would do it. I would plug the triaxis into the Decimator, and from it, into the power amp (all plugged up mono). I would also probably turn the power amps volume up fairly hight (in hopes of getting more power tube tone). Then you will plug the power amp into the Palmer (make sure it's set to give the amp a load!!). From the Palmer plug into the soundcard. Plug your monitors into the soundcard, and you're all set.
If I were you, I would try this setup with and without the power amp. The amp is not necessary at all, unless it just adds that little extra something to your tone. Just thinking about that power amp plugged up to 2 4x12 cabs gets me excited and makes my ears hurt! That is a rediculous amount of tube power! :eek:
As far as the Eventide goes, I have no idea. I alway's use the effects included with my recording program.