ARC vsi 75 vs. Pass int 25

i have the pass xa25 as well as arc ref 75

arc better at imaging and fleshing out midrange, pass better at bass depth and drive

my speakers are spendor sp100 r2's, harbeth monitor 40's and proac d30r's - none too low impedance, nor hard to drive

That is easy for mr ARC VPI 75. I have owned Pass designed amps for nearly forty years, but the ARC tube amps are natural and incredibly beautiful… I now own all ARC equipment. 
 

Now if you are into have a really hard load the Pass might be better. But for musicality ARC. 
 

Neither one would be a bad choice.