ATC SCM 40 question

Hi,

I recently bought a pair of ATC SCM40 speakers. I have them placed in a room approx 12ft sq. They are on the back wall, seating on opposite side. I can't move the speakers into the room or move the chairs into the room as I barely got away with buying these and can't encrouch any further, the missus was not happy at the size of them!

Anyway, they sound pretty incredible a lot of the time, but I've noticed on some recordings, not necessarily bad ones, just they can come across a little shrill and sharp, like the highs are overheated somehow.

I'm driving them with a PS Audio S300 Poweramp, that is being controlled by an RME ADI 2 DAC. 

I've tried messing with the dsp settings on the RME but I just can't seem to ease the issue.

My question is, does this seem like an equipment issue? Or maybe a cable issue?

I don't want to end up spending serious cash upgrading the amp or dac if that is not the problem. But I know the SCM40's need a lot of juice and the S300 only has 140w per channel, and the recommended is 150w. Or is that just a top end volume concern? I'm already looking at the Hegel H20, I can't get the ATC poweramp as I don't have the space for it.

Also I was looking at the Anthem STR Preamp. Something that might calibrate the sound better for the room. Maybe a cable upgrade?

Anyway, these are just my rambling thoughts on an ongoing issue, any advice at all would be much appreciated. I really want to solve this as when these speakers sing, they really sing!

Thanks
M