ARC LS25 with PASS X250 - bad match? Seems bright.

I just switched my amp from an arc VT100mkII to the PASS X250. Upon doing so, I heard more brightness and even harshness in my system. I have heard that the PASS amps are not bright, so I am suspecting either a system mismatch, or that the X250 is more linear and is revealing another source of brightness in my system, that the tube amp perhaps was masking.

Rockport Mira Monitors
Wisdom SCS Subwoofer
Audio Research LS25 mk I
Bryston 10b Sub crossover
Cambridge DacMagic
J.A. Michell Tecnodek
Dynavector 10x5
Cardas 100b microtwin balanced interconnects
Cardas Cross speaker cables

I am having a feeling that maybe my source components are not up to par with the rest, and that may be the cause of the harsh brightness at times. Or, that the PASS does not like the ARC LS25. What do you think?

Do you hear the brightness with all your sources equally? There could be a potential impedance mismatch. ARC suggests that the minimum load the LS-25 sees is 20 Kohms, abd the X250's input impedance is 22 Kohms. So you are threading the needle. Do the X250s have single-ended inputs or only balanced (XLR) inputs? I ask because the output impedance of the LS-25 is higher via balanced vs. single-ended connections, so it could have less control over the X250 via balanced connections. My guess is the LS-25 has a highish output impedance in the bass region and you are getting attenuated bass as a result of the mismatch and so the sonic picture sounds tipped up and bright. If all your sources sound equally bright, my bet is that is what's going on and you would be better off switching back to an ARC amp or if you want to stick with a SS amp, you should get one with a minimum input impedance of 50/60 Kohms. Of course the best way to do it is to audition whatever amp you get to replace your X250. The other option is to replace your LS-25 with perhaps a PASS pre amp that has a very low output impedance and keep the X250.

GGood luck.
I don't know the VT100, but the X series Pass amps, in my experience, will produce more treble energy than many tube amps. I recommend you live with it for a while and experiment with small adjustments to your system and see if maybe you can get it to a place you like before making a major change.
The Dacmagic is known to be a little on the bright side. You can look for a warmer sounding digital cable, but the fact remains your DAC is not up to the level of the rest of your system, so the sound will always be compromised even if you tame it down. Also, you never know what you will get when mixing amps and preamps from different manufacturers. If you are still not satisfied after improving your source you should either go back to an Audio Research amplifier or get a Pass preamp. When the amp and preamp are matched there is always a rightness to the sound that cannot be achieved by mixing brands.