McIntosh Mono bridge vs mono parallel connectons?

I am thinking of buying a 2nd MC2150 amp to use as mono blocks. The 2150 provides 150watt/channel in the standard set up. If I wanted to double the power with a second amp - the manual shows a mono bridge connection and mono parallel conection with one program source. So which is right - or am I barking up the wrong tree??? I am driving older Thiel CS2.2's and when pushed I do not get the depth or color I am looking for. My front end is a Mitchell Gyro SE with McIntosh C32 for my preamp. Anybody with experience with this set up would be a great help.
I have run an MC7270 and MC2255 as a pair of bridged amps into an older pair of KEF's with impressive results. I was answered by the McIntosh factory to run in bridged not mono-parallel but they never gave any theory as to why. Last, is the increased power seemed to shorten the preamp volume sensitivity which may be annoying in some situations. Your C32 is similar to my C37 and while it was never a problem it was difficult at times to quickly/accurately adjust the power levels.
This is what Mr Poon of Monarchy Audio also recommends for his monoblocks....BUT, why make the mono bridged an option if its less than optimal....