This is kind of interesting... I bought a 2.7 ohm Hot Plate for the VK. It lets me crank the amp into overdrive at volumes that are sane for my music room. (I may not get a chance to try this on stage for a while, but that's another story...)
Lately I've been playing clean more often than not. But I still wanted to be able to kick in some extra distortion for hard-rock rhythm and leads, because the VK can't quite get there by itself. If I'm willing to open up the amp without a Hot Plate, I can get close enough - the speakers break up nicely and all that moving air hits the guitar just so. Of course, that's well into earplug territory.
So I bought a Boss DS-1. It sounded OK at the store with a Les Paul and a Super Reverb, so I figured "why not?"... It was used and inexpensive. When I got it home I left everything the way it already was on the VK - volume up to 4 and Hot Plate dialed down to where the room volume was around 95 to 100 dB. And it sounded great!
But here's the interesting part... I got to wondering why people felt the need for mods on the DS-1. I decided to turn down the amp, turn off the Hot Plate and see whether that made a difference in the sound. Boy, did it ever! Where the DS-1 was smooth and fluid with the amp on 4, it was edgy, harsh and brittle at the same room volume with the amp dialed down to 2 - that's the point where the VK is totally clean with humbuckers.