The MV50 has a tube preamp. The high-end amplifiers have tubes in the preamp section as well as in the power section. So it's not a pure tube amplifier, but having a tube just in the preamp section provides a warmer sound than just a solid-state preamp section.
This unit has a speaker out to hook it up directly to a speaker and it has a line out that does speaker emulation. The line out would be what you would connect to your amplifier's input. I would suspect that the sound would be an improvement over a purely solid-state amplifier. I have used this unit with my old practice amp. It did improve upon the sound of a very cheap solid-state practice amp. but the sound quality was limited by the quality of the speaker in my cheap practice amp. When I plugged the MV50 directly into one of the speaker cabinets I use for my PA system, it sounded great. But that has a quality 15-inch speaker. I would assume that your amplifier probably has decent quality speakers in it. So I would think the quality would be quite good there as well. Remember, it's not a pure tube amplifier but it's the next best thing to it, since it at least has a tube preamp.