This is not the answer you're looking for but here goes: SERIOUSLY consider better/different speakers. I'm not saying more expensive either. Whatever you are looking to improve sonically, I'd bet it is from what you aren't getting from your speakers, which probably are what dictates the overall sound more than anything in a system. Bose are really over hyped and generally provide substandard sound quality - flat, congested and not very accurate. All the tricks they use (over-wide dispersion, backfiring, magical bass enhancement, etc) just go against good audio design and as they say, if it sounds to good to be true, it usually is.

Again- I'm sure this is coming off as just being snobby, but it's not I assure you. It's not about price or anything, especially since Bose products never were cheap anyway. It's just that they are one of those brands with a marketing department that works a little too good for the customer's own good. There is a lot better out there for the same money, or less usually.

The Dynaco ST-70 power will almost certainly be sufficient for your current speakers. I don't know the efficiently rating for your particular Bose models, so you can check your manuals to double-check.
The MC 2100 amps - I don't memorize model #'s, but I think those are McIntosh, right? If so, then they are well-regarded and you'll be happy with them, IMHO.

Aaaah- good plan! Carry on and have fun. I built some DIY Pro-Ac towers this year and not only was it really fun and educational, they sound great! Like making a good meal that you get to keep enjoying...

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I've heard this many times about bose. My plane of attack is amplification first, then some scratch built speaks. I can work on an amp inside woodshop is outside.

Your MC 2100 will just not reach its full potential unless you can find a speaker that will do it justice. No offence but I doubt you could build one that good. Bose won't come anywhere near unless you have a 901 and that too with a lot of effort and only with the right room. Buy the amp and play around with the speakers you have, save some money and buy some decent used speakers or new e.g Totem Arro or Acoustic Energy's RC-70.