How can I tell if I am overdriving the amp or the speakers?

"The amp is 250 x 2 into 8 ohms," and the speakers are rated at 90?

I wouldn't think it would be the amp running out of power.  I would think the speakers are just trying to work to hard.  But I also think that the room acoustics suggestion has merit.  Back in the late '90s & early '00s, I was in the mode to be pretty much be playing my stuff to loud all the time (& the stuff I was using wasn't cheap stuff, either). I would be jamming out to ear bleed levels in the living room & thinking that I was at the cusp of clipping, but when I'd go out on the back porch to barbecue or whatever, everything sounded sweet & clear with no distortion.  

I don't think you are "overdriving" anything. I think you mean pushing the speakers or amp to where they start distorting.  It would get really, really loud before that happened.  some songs are recorded with too much treble/upper midrange and come across harsh on an accurate system so make sure you aren't testing with the same song every time.  Some amps are harsh.  I have a friend with the same amp hooked up to some Raidhos and he plays it very loud with no harshness.  His system sounds better than mine.   I suspect the speakers are a bit harsh.  I have a tube amp and had to swap out a few tubes to eliminate harshness but you can't do that.   --Jerry

@spatialking ,

Lets see, no warning light. No blown fuses, oh and I have AQ, 8’ Rocket 88 speaker wire.

JD

@grannyring ,

15’ 6”x 20’ room with openings on every wall. Front end is either an Oppo, Audiolab 6000CDT or using upnp to a NAS. 8’ runs of AQ Rocket 88 wire. Speakers are 7’6” apart with my listening position at 7’6” and no toe-in.

JD

And while I am play some tunes loud, It’s no where near face melting volumes I’m talking about. I’ll put a meter to it tomorrow and give some numbers, but I’d be surprised if I was much past 85 dbs.

JD