M22ti to M50ti isn't an upgrade or a downgrade...it's a different sound.
How big is your room upstairs that the M22's are currently in? If it's not that large, then perhaps replacing the M22's with a larger speaker wouldn't make sense.
If it is large enough for towers, and you really like the sound of the M22's, get the M60's and move the M22's downstairs.
If your current room is perfectly suited to the M22's you have now, I'd just get another pair of M22's for in the basement, or even a pair of M3tis's or M2i's. It doesn't sound like this basement setup is going to be for critical listening. Why spend more than you need to?
