I wouldn't spend the money on the little Adcom either. About roughly twenty years ago, I came across one already done. I can't remember if I bought it, or if it was part of a trade back then. Another thing, that amp is 60 wpc @8 ohms, I believe. The one I tried was the 545 or 555 series. It may have been done by a well known (for Adcom owners) called Musical Concepts, if memory is correct.
The sound was better that stock, but it sure didn't compete with some of the better stock units back then. Also, the resell value was close to a stock one. The main power supply capacitors don't last as long on some amps like they used to. Those main caps are unpredictable anymore nowadays, though. Some amps had bad production batches go bad fairly quick. If those go, then you'll have to put more money in it, or sell it as is, at a loss. I don't believe those will be replaced by them. Plus all the other older parts will still be there. Even with this aside, I still wouldn't put $299 in it.
I think upgrading to something newer makes more sense. I'm not familiar with the newer ones for any recommendations. But, something under 10-15 years old may get you more for your money, may sound as good as the upgraded one (possibly better?), and may last longer.
I'm not familiar with your speakers, but make sure another amp can drive 4 ohm speakers like the Adcom can. I looked on the net at your speakers, and they do need an amp capable of running 4 ohms speakers all day long. Maybe go with a little more power than the 535II too. One person wrote a small review, and said your speakers are a little bright. If they're correct, make sure a newer amp isn't bright too. That would be a bad combination in my opinion. Try to find some reviews, and shop around for something newer, is what I would do.