Wowsers! You inspired me - Many many thanks.
(Btw, was that testing their free download or have you bought from them?)
On the strength of your post I decided to check out 3rd-Party IRs for use with my Yamaha THR100HD. The amp comes with a utility program that lets you mess with various things, one of them being the IR associated with each amp model on the two amps. The IRs are used on the headphone out and the balanced XLR outs.
By default they've got their own IRs installed - a 4x12 for Lead, etc, etc.
To start with I didn't like the DI'd sounds - they were too different to what I was getting out of the speaker cab in the room I was in. Then I spotted they had IRs for their own speaker cab... so I plugged those in and was very happy for a while - the DI'd signal was pretty darn close to what I'd dialled in using the cab.
But now I've got more used to dialling in the amp... well, to be honest, I'm not sure I need the cab in my little room. In the living room, with loads of space (and the neighbours all out), the THR 1x12 kicks out some seriously good noises. Even the missus is impressed. But in my little studio, it's a bit unmanageable.
I'm starting to hear new sounds in my head, and they're 4x12 sort of sounds. But the THR's IRs for 4x12s don't move me...
So on reading this post, I went on a download hunt. I got the Ownhammer free set, and a bunch of others. Last weekend I sat on the sofa with the laptop, THR head, and headphones checking out the stuff I'd grabbed.
WOAH!!!! 
The Yamaha IRs are "OK" but some of the things I'd downloaded were AMAZING. Again, even the missus was impressed. She was very dubious as I was forcing the headphones on her, but she was actually amazed when I AB'd the Yamaha IR I'd been using and one of the downloaded 4x12 with SM57 IRs.
Anyway, I'd not had time to do anything else until last night. I had to tidy up the living room a bit, which meant taking the THR head back up to the studio. While I was there, I thought I might as well plug it in and see what the DI is like through the monitors now...
...I didn't get much more tidying up done!!!!
It sounds utterly utterly GORGEOUS - and I don't even know which IRs I'd left plugged in!
(I think it's the Ownhammer ones - they were the last I downloaded)
Hopefully, I'll get some time this weekend, I'll plug the laptop back in and check out what it is I'm using on the Crunch and Lead models... and is there something even better?
I'm now going to be looking for an open-backed 2x12 IR that I like. My favourite ever amp was the JMP 2104 MV 50W combo - I never actually owned one, but all of my tone quests ever since 1980 or so have been leading to that. I suspect that the THR's Lead amp, with the "right" 2x12 IR is going to put me there...
