Amp and speakers combo- Magnepan MG 1.6/QR

Right now I am running the following system

Pre is NAD 175
Amp is a NAD 975-140 wpc
mac mini with music fidelity vdac(all music is now played thru this)

Front speakers are the 1.6's
MMGC center channel
MMG back speakers

Now when I watch a movie or have a TV program on in 5.1 the system sounds good.

In Stereo mode it might be a little bright on some music and on others very nice. The placement of the front speakers are fine, nice sound stage and good overall sound.

three selections of music that I keep going back to
US blues - Grateful Dead
Deacon Blues- Steely Dan
Jesus Just left Chicago Govn't Mule

I would like to take some of the brightness off. Suggestions on where to start?

Oh and I tried a set of Tyler Linbrook Supers, but I am really a planar man

Thanks in advance for the help