...I don't think every Yama from 90's is great, right? ....
Correct. But, they are all good.
It's not easy to put together a great stereo. Most of us are gear heads. We love reading specs and reviews, just as well as listening. We're like baseball fanatics that can cite any statistic off the top of our head.
I still don't know your budget. That would change everything.
All of this info is on this site but would require months of reading. I'm going to give you a highly condensed history lesson. Feel free to ignore it. Others will step in with contradictory information. Welcome to the subjective opinion.
Here is my opinion on brands and models:
1965~1973 was all about Marantz. Their top models of the era still sound good today but all of these require recapping and some other mods. Worse still, many of them have been repaired gorilla style and need to be unrepaired by someone who knows what they are doing. While good sounding, these receivers don't put out the power a contemporary audiophile would expect.
1974~1981 was all about Pioneer, Sansui, Kenwood (in that order). IMO, Kenwood was the best of the three at the start of this era and the worst of the three at the end of the era but it doesn't matter. All three are good. Power was starting to become plentiful, even by contemporary standards, but only the top units. Most amplifiers of the era were in the 40 Watt range and that isn't enough for what you're trying to do with those Bostons. All units from this era benefit from rebuilding, even if they are functional. Max performing these units, at this point in their life, is more likely to cause failure than newer units because they are 40 years old and have been subject to countless heat cycles. Worst still, this seems to be the most popular "golden years" era, so the top units of this era go for tons of money.
The top Sansui and Pioneer gear goes for ridiculous amounts of money, these days. These pieces are probably worth it, for the aging audiophile like myself, but they are no bargain for those who don't cherish their history.
Kenwood is the only popular brand of this era with some value headroom, IMO. The problem with Kenwood is they don't have a lot of resale so aren't necessarily worth a professional refurbishment.
This era was so good, any of the top integrated or receivers of this era can be considered excellent as all brands were trying to exist in the era of a massive stereo arms race: Yamaha, Onkyo, Sony, etc.....
This was also an era that had some excellent boutique brands but, again, they are sought after and there is no value in them.
1982~1994 this was the era of Yamaha, Sony, Harmon Kardon (and some others I'm probably forgetting).
Specifically, the Yamaha separates were all good (ie: preamps: C70, C80, C85, etc. - amps: M60, M70, M80, M85, (more reliable after this) MX-600, MX800, MX1000). There isn't a lot of value in these series and the early ones need rebuilding. Later ones generally do not. Capacitors were just starting to get much better in the later 1980s. Prices on this gear are starting to go up. They are losing their status as forgotten top performers.
Most of the Sony ES line was good in this era. That includes ES integrated amps and ES separates.
Harmon Kardon was good in any era but they got *really* good in this era, IMO. Everything they made was upper-middle end, or better. Something like an HK PM665 might be a decent integrated for you.
Kenwood had a few excellent pieces trickle into this era but, by then, the quality was gone from most of their line. Specifically, the "Basic" line was really good: C-2, M-2, etc. They had a few outstanding, massive receivers trickle through to this era, also.
Hafler also has a few decent pieces from this era that can be had on the extreme cheap.
Luxman, also excellent in this era.
1995~onward This is the era of home theater. Stereo gear in this era is generally top quality and expensive. Home Theater gear from the start of this era is not all that desirable, at this point. This is also the era of lousy, Chinese, capacitors. The failure rate of these Chinese caps from 1995~2005 is 100%. Typical lifespan of these caps was just a few years. As production moved from Japan to China, equipment became unbearably bad in longevity. All of these devices from this era can be revived with decent caps and some competent TLC but few are worth the effort and expense.
From every era, there are good pieces from pretty much every brand. That includes Radio Shack (for real).
If you want a great deal, watch for estate sales and stop by the Good Will. If you want totally reliable gear, get a piece that has been rebuilt by a competent technician or look for the 1990ish equipment that had better quality components, like the Yamaha CX/MX series. There isn't a ton of this stuff but it's out there and is great value. If you can replace capacitors and do minor repairs, you will be looking at a massive inventory components. Keep in mind, some amplifiers from back in the day used modules which are no longer available and require electronic kung-fu to repair if those modules go. The modules generally don't go, so it's not a huge problem, but keep it in mind.
I'm going to guess you probably won't be happy with less than 60 Watts, particularly with those Bostons. You will probably end up taking the best of what you can get for power but you should probably look for 100+ Watts and, unfortunately, that is what everyone else is looking for so you have to be clever to find deals.
Keep in mind, nearly everyone on this site is going to tell you, "Get what I have. It's the best." Audio is a life long pursuit of finding specific equipment you like for nostalgic reasons, pieces that look impressive, pieces you have heard and are impressed with, and pieces you find for next to nothing so try and are impressed with (there is far more good equipment than bad).
One more item: You are probably a single source guy so you can consider buying a power amplifier and completely forgoing a preamplifier. Use your computer for volume control. This configuration works and sounds excellent. Something like a Yamaha MX-600, MX-800, Kenwood Basic M2, M2a, Harmon Kardon HK-775, etc..... would provide a lot of extremely nice sounding power. Any of these amplifiers would undoubtedly cause you to develop new respect for your Boston speakers.