The last couple of weeks I've been enjoying the Mercuriall '59 Tweed Bassman plugin. It's harmonically rich and gorgeous.
Why mention this in the Fractal thread?
Well...
I went back to the FAS '59 Bassguy model and it wasn't quite doing it for me, for some reason, even with the same IR I was using with the Mercuriall plugin.
So I decided that the Bassguy model was perhaps biased a little cold. I whacked up the grid bias to 68%* (no chance of wear on these tubes) and there it was! So much better.
For fun I also swapped in 5881 tubes, over the 6L6s; but that isn't really required to get the big improvement that I experienced.
It was an improvement to me anyway; It's a personal taste thing. Maybe you'll enjoy that model stock. ** shrug **
* IIRC, the bias was set to something like 48 or 49% as default.