Steve, 0,7ohm looks incredibly low to me. R U certain of that figure? If so, you'll have to mod the amp to take that sort of load (unless this has been provided for already), and, geberally, tube amps are extremely unhappy with very low loads.
I'm not sure what parallel mono mode is; if it's bridging each stereo amp to amplify mono then the load impedance the source will see will be halved UNLESS Mcintosh has a different design provision (which they'll specify).
Amp sensitivity: shouldn't change, but again, I don't know the effects of bridging on yr amp (McIntosh probably specs this in the manual).
Matching the tubes: let's not go overboard:) As long as the tubes on the old unit aren't severly tired, it'll be OK. In any case, you'll hear the differences if any. UNLESS you mean, should the two amps be using the same brand of tubes -- in which case the answer is yes.
I'm not sure what parallel mono mode is; if it's bridging each stereo amp to amplify mono then the load impedance the source will see will be halved UNLESS Mcintosh has a different design provision (which they'll specify).
Amp sensitivity: shouldn't change, but again, I don't know the effects of bridging on yr amp (McIntosh probably specs this in the manual).
Matching the tubes: let's not go overboard:) As long as the tubes on the old unit aren't severly tired, it'll be OK. In any case, you'll hear the differences if any. UNLESS you mean, should the two amps be using the same brand of tubes -- in which case the answer is yes.