I think the best usage you can do with this amp is operate it yourself, although it does have some value as a vintage amp, you will have to add a bit of $$$ to get another unit that has similar functionality. If you still want to sell the beast, eBay is always a good option.
To adjust the voltage levels, you need a small format yet high quality mixer, the good ones start at $80 such as the Mackie 402-VLZ3, very small and will do exactly what you need, get you the voltage level you need plus convert these unbalanced RCAs to balanced XLRs. Connect it all and be happy
Ya it doesnt have good imputs. It has 3 screws on the back for imputs. But i will try a mixer. I may put it on ebay aswell. I dont know what its worth really