Which to Switch: the Mac or the Act?

We have been very happy with the system for a year with no complaints. But, its been a year without tinkering and we're feeling the "what if" itch that keeps this industry in business. Right now its an all American mix and match potpourrie:

ARC CD8
CJ Act 2 Series 2
Pass XVR-1 (external cross-over)
McIntosh MC452

I am considering either: (i) replacing the Act 2.2 with ARC Ref 5 SE; or (ii) replacing the MC452 with Pass X250.5. Can anyone comment on what we might expect by way of change? How the sound might differ, pros/cons, etc? For example, re preamp, will there be audible synergies by mating the CD8 with its ARC brother Ref 5 SE (presumably yes, but enough improvement at the margin)? Or, re the amp, we like the MC452 a lot (and it would go into a second system, not leave the premises), but we have never had Class A in the house(the X250.5 is Class A up to 15 watts), and the folks at Pass were so helpful in guiding me through the XO set up that I'd simply like to give Pass the business (space constraints rule out the X350.5).

We listen mostly to rock, jazz and Broadway at moderate listening levels, but do crank it up on Saturday nights. Prefer slightly warm side of neutral(emphasis on slightly). Speakers are Linn Akurate 212 with JL F112 sub. Any input is appreciated.