Yo,
Yesterday I happened upon a thread in another forum where a player (a very good player, from what I've heard) said he uses one, and sometimes two, Valvulators in line before his POD. Here's an excerpt from that thread:
"This is why I use the Valvulator with my POD-XT'x & Bass POD-XT. In fact I have two Valvulators, one has an Amperex BugleBoy & the other has a Telefunken Long Plate NOS tubes. By changing the tubes you can affect how the Valvulator affects tone and you playing dynamics"
Interesting -- maybe I should experiment with that application myself. I never would have thought of running the tube device before the modeler...
There are also a number of relevant discussions at StompBox.net The main suggestions from that site were 1) run an EQ post-modeler to notch out the offending frequencies, and 2) always run a modeler through an FRFR (Flat Response Full Range) amp, such as a keyboard amp. However, in a separate thread on that site, it was pointed out that the XTL might be an exception to the FRFR rule, and actually sounds best through a
tube power amp. Sounds like experimentation is the only solution with this modeling stuff...
Bert