Solid state warm up?

I only meant to qualify my subjective impression of the VK-250SE by saying that I never left mine on 24/7.

Again, you've offered no justification for your claim that the 250SE can't adequately drive these speakers.

I've no doubt that the OP is hearing what he is hearing, and like him I didn't particularly care for the overall sound of this amp. But I don't think that any technical shortcoming of the amp can be blamed.

Not needed to leave it 24/7, a 30-40 min warm up is fine.
SS amps get better over days though.

It's not the blame that the amp can't drive speakers. Certainly it can, but it's a fact that there are amps that can drive these speakers better than VK250SE and the llist is HUGE even if taken the same budget point.

SS warm up? Tubes yes, SS maybe 15min tops. Your not going to get a dramatic improvement from a warm up. It's probably your setup and the listening room.

I have yet to see a solid state device of any kind that did not benefit from at least 24 hours of warmup.

Certainly in this case its worth a try- if it makes no difference then don't leave it on all the time :) But I think you will find that it does make a difference.

Now- will that fix the mushiness at high volume? Hard to say. If it does not, its probably not because of insufficient power; if a speaker needs more than this amp makes then the speaker is simply impractical for the real world. But if there is not enough filter capacitance in the power supply (or if the filter caps in it are having some issues), mushiness at high volume will be the result, regardless of the power the amp makes or how long it is left on.