You sound like you know what you're doing (way to go Dad!) but have to ask since you didn't say - did you re-run the receiver's speaker calibration after the room was redone? If not, that might help; but I also think you're on target that the vinyl/carpet swap is the driver here.

If recalibration isn't the problem, then then only other thing I can think of is that the M80ti (all the *ti's) were thought to be a little more harsh than what came after (the ti's are a few generations back). That may not have mattered when you had carpet dampening the sound, but may be exacerbated now that you have reflective tile. So you might consider trying out a new v4 version of the M60/M80s.

I didn't know your Dad, but it's always nice to see generations stopping by.