What about a preamp that offers some emulations of pedals that will provide some grit or amp emulations like an SVT?
I play a TCE BG250 which does have it's own "Tube Drive" circuit for adding some warmth and/or grit and got me close to the Ampeg tonality I've typically preferred. But adding a Zoom B3 as an add preamp was a game changer. My buddy and guitarist has an Ampeg BA112 in our rehearsal space and adding it to that amp has him looking to pick one up as well.
No 1x15 combo is gonna sound like a 300w tube head through an 8x10 cab but it does capture the essence of that throaty SVT sound. The same with the B15 model and the Eden WT and the rest. Each is like a snap shot of that amps basic tonality. Cab emulations can add to that with some and not at all with others when played through the amp itself but are very useful through full range/flat response speakers and a FOH PA.
They're $200 new but used B3s go for around $120 or less. It may be something worth trying to see if it can give you what you want. Cheaper than a new rig and if it doesn't work out you won't have much trouble getting your money back out of it. It's also a handy backup for your rig in the event it should ever fail during a gig. Or you could even use it stand alone with a powered cab you like. Just thinking outside the box here.
