@Echopark
I would say that you are correct in thinking the out of phase scenario is the thinner sound. My guess is the “boomy bass low-end” is caused by two preamp signals hitting the phase inverter at the same time. Have you tried adjusting the eq and/or gain on the preamps?
Edit: Not sure...
No offense meant to the Peters from me either, just having fun! I was really interested in the mini when the prototype pictures appeared but ultimately ended up with a VH-2. I'm sure the mini will be awesome when it hits the market! And yes, Diezel rules!
Not my video, but I tried both in the same guitar. As @FLUXX noted, more headroom in the X series. Also, I found it to be tighter in the low end, with more clarity in the highs.
The Mesa cabs (in addition to being rear-loaded) usually have 8-ohm speakers instead of 16-ohm. This might also account for a smoother top end. I know that with a Mesa 4x12 Traditional, the Treble and Presence need to be goosed quite high on my VH-2 to get it where I want.
I've read/heard that Channel 1 of the VH2 is actually based on Channel 1 of the Paul, while Channel 2 of the VH2 is a slightly gainier and more "modern" sounding version of Channel 3 of the VH4.
I'm using a Mesa 4x12 Traditional (rear-loaded 8-ohm v30s) with my VH2. I have to crank the treble and presence pretty high for channel 2, otherwise it is a little too smooth for my taste. I imagine this would be less of an "issue" with a front-loaded cabinet.
@angelspade
Besides using 6L6s, you might also try a quick modification by moving the negative feedback from the 8ohm tap to the 4ohm tap on the output transformer. You can find details here:
https://www.rig-talk.com/forum/threads/collection-of-all-kind-of-diezel-modifications.208989/#post-2315750
I was originally waiting for the mini, but ultimately went with the VH2. The amp has excellent Channel/Master controls, capable of “restroom volume”. If you can deal with the size and weight, don’t let the 100W rating scare you off!
Do you know what year the fellow owner's VH4 is and how the tubes compare to your's? If I'm not mistaken, Diezel revised the amp's circuitry at some point (2012...?) to make it brighter. I will have to defer to the experts for the exact timeline.