For an IEM gig where you want honest to goodness real Ampeg tone with no compromise, I'd look into the REDDI. Straight up DI with a tube and actual power and output transformers. More expensive than the VT yes, but does a dead-on cop of a clean B-15 set flat and run through a speaker out DI. Not a simulation but the real thing. Done two gigs on mine and became a royal tube snob again and lost all desire to use a cab mic, and can't stand to use anything but my tube Ampegs as a monitor because I get jealous of the crowd. Yeah, it's expensive and heavy as far as DI's go, but it's so noticeably better to anyone with half an ear.
All respect to the VT, but you really can tell the difference. 2d vs 3d, except this is a 3d that isn't annoying and requires stupid glasses.