Here's what anyone who is using an HD500 + DT25 needs to know:
Be prepared to ROCK!
No, in all seriousness, thank you all for the awesome responses!! I got to plug 'er in last night, and picked up an amp stand before rehearsal. This little baby is perfect for rehearsal / gig levels, it absolutely holds it's own with the other guitarist cranked up through a Fender tweed / blues deluxe 40watt.
As far as patches, I had loaded everything on my HD500 that I could find on Customtone that would be preset friendly to the DT, and after about two minutes, jumped to blank patches, and set up a few very basic tones - noise gate first, then wah. Comp FS1, Distortion FS2, Reverb FS3, and Delay FS4.
Within that framework, I just saved into a few banks, and tried switching around the amp choices, using the 'PRE' versions of a few amps I knew I would be comfortable with - JCM800, Plexi, JM45, DIvided, etc. It's gonna take some serious digging in to dial in some of the Fender / Vox models, but overall, I was *REALLY* pleased with using the guitar>HD500>L6Link>DT25.
It's a nice touch to be able to get a patch mostly there, then be able to just tweak a dial on the DT25 to adjust a little of this or that. Some of the amp models are blasting loud right out of the gate, and others take a little coaxing. Working the channel volume, the DT master volume, and the HD500 master volume, you can dial in the right amount of clean headroom vs. grit, and get the speaker volume where it needs to be. In particular, the wahs sounded stellar thru the DT25, and it does a nice punchy thing when you stack compressor boost, drive, and channel drive together. It always sounded good doing that with just the HD500, but something about how the DT25 handles the crunch, and the tones makes me very pleased. You can really get alot more touch sensitive tone using the tone stacks and volume on the guitar, where your fine tuning is at your fingertips, your rough edits on the amp, and the deep edits on the POD.
Very encouraged by finally pairing my HD500 (which I've had since 2010) with this amp.. I used to prefer the 'full range' approach to using Studio/Direct output modes, since i was always running the HD500 into the FX return of a few solid state amps. With the DT25, you get the proper amp tone / volume / vibe, and letting the DT25 handle the board feed via the XLR out, it's just spot on. Add a mic to the front of the combo, and your soundguy has all the options he needs to make you sound great.