Balance on Tube Amp

both XLR and RCA ins and outs

manual volume control, individual L & R

Schitt SYS, Switch Your Stuff, 2 Way Switch with Potentiometer, use a pair of them for independent L & R, $49. each

Sounds like you do not have a preamp. There are multiple reasons to use a preamp, balance control is on of them.. a good one will improve the sound quality significantly in nearly all systems.

If you did not experience an imbalance with your previously mentioned amp - perhaps there is something wrong with the "recently purchased" unit.

DeKay

There aren’t many integrateds with volume balance capability. I have this issue and was going crazy with all the vocals shifted left, solved with the PSAudio Stellar, then decided to get tube/SS hybrid and finally found Mac MA352.  That Schitt box might have widened my horizons had I known about it but that’s ok. If you get your hearing checked you might be surprised. A balance issue can be a hidden problem, especially if you are one of those who is always straightening pictures on your wall.