Likely culprit for harshness at higher volumes?

I would try decent (not necessarily expensive) analog cables instead of the Toslink first.

It's your speakers.

From a review: "The overall sound can get a little grainy if pushed too hard"

perhaps clipping.
Source music is awful, as has been noted by Shad, above.......look up 'loudness wars' if your want more info.

Also, Since speakers so not have watts, I'd simply ignore that rating. Good, loud, dynamic music demands a lot of an amp. Maybe it's just not passing muster.

Hi guys,

Thanks for the good info. I connected the CD player to the pre-amp using non-brand but what seems like otherwise decent, gold plated RCA cables using the analog output/inputs. To my surprise, while the harness is still there at higher volumes, since I was listening somewhat critically, the analog actually sounded a noticeable crisper and brighter than using the toslink. The toslink sounded slightly muffled in comparison. I'll get better cables next week to connect the pre-amp to the amp; maybe the combination of using CD analog outs and better pre-amp/amp cables will help.

Anyway, the harshness is still there regardless of toslink or analog.

So, based on the comments so far, that leads to speakers and/or the room (ignoring the cables for now). I'll try using the Q10's I have and see if that makes any difference. Will report back again later.

The room is fully carpeted but the drywall walls are bare and the cabinets are either dense wood or glass so reflections are probably possible.

As a solution put ferrite claps on the interconnects from the preamp to the amp.
get four snap on ones from Radio Shack and put one at each end of the interconnect from the preamp to the amp. about five inches from the RCAs at each end. (you see ones similar on various computer cords now and then)
If they are too loose when clamped down, wrap some tape on the wires to give the wire body enough volume to keep the ferrites from sliding around too much.
The Ferrites should help with the HF glare.