My Yamaha A-S500 is driving Monitor Audio floor-standers of recent vintage (rather petite model Silver 6) - and the sound quality is very good indeed. Addictive even. The Yamaha receiver amp sections, unfortunately, are not the same amps as their integrated models with a tuner added as some suppose and reasonably so, as it was done more often in the past - NAD certainly did. I believe the OP would love an A-S501 driving his Klipsch. Or step up a little closer to that grand for a 701 or 801. Nice.
While tube amplification is quite beguiling, I'm more the lock-and-key sort. A good solid state amp requires no maintenance to speak of, and less trouble-shooting is good for my soul. Never was a tube-roller, either. Just finding a matched quad for a custom ST-70 that actually all glowed properly proved to be enough tube-rolling for me. Gimme transistors, please. I prefer listening to music over repairing, replacing, or fiddling with gear, though I do like the remote control fiddle.
So, I wouldn't know what tube integrated amp to recommend and will leave that for those smarter about it. My experience suggests that a grand may not get me all I want from tubes. Best tube gear I ever heard always came with an Audio Research Corporation logo, and big tickets.
For solid state at under a grand I like Yamaha because the company has an excellent track record of building high quality at reasonable cost because they can sell more units than many brands. Want a really good acoustic guitar? A three-to-four-hundred-dollar Yamaha will provide a professional sound quality. They make wonderful pianos, too. I know those Yamaha guitars are hard to beat for the price. I own two now, and still pick one up now and again... they sound great, really good tone. And use some build techniques usually found at a higher price. And they sell a lot of them. The more units that sell, the lower the price can get.
Of course, they have a long history in audio, too. Some fine gear over the years. They still have the advantage of selling more than most audio brands, and they've always been above average with quality control. I believe their technical experience and long history of good, reliable product makes them hard to beat for affordable integrated amps, too. When it comes to the A-S1100 at $2500, I'm looking elsewhere, but near or under a kilobuck I put 'em on the shortlist.
I like Cambridge Audio, too. But I don't believe they are built better than the Yamaha int-amps priced near them, or maybe even under. However, I've not heard the Cambridge int-amps, so can't comment on their sound quality. Do have a little receiver Cambridge that I enjoy sometimes.
I'd also check out Marantz at the price. Used to swear by NAD until I bought their $1k preamps 160, then 162 and both quit after a few months of warranty expiration. Same problem, failed logic circuitry, which was almost guaranteed to recur (from my 100% failure rate perspective) - to fail again. When they failed under warranty, the manual (and the Company) treated the subject as normal, instructing to leave it unplugged for a specified amount of time, plug power cord back in and it is reset. And it is, the first twenty or so times you have to go through this, but then it relieves your stress by refusing to work at all; two weeks after the warranty expires so does the product. An experience that weakened my faith in the company. I once owned nothing but.
I have considered replacing my A-S500 with a CXA-81, but the sound is so good now to me that I have trouble believing I'd hear any difference. If I try one, it will be easily returnable. However, I just keep losing that need-it-feeling whenever I listen back there.
Of course, the A-S500 was considered by many to be the sweet spot in the line. I don't know how well the current A-S501 compares with it - could be even better, for all I know. Picked mine up from an AKer who asked $200 a few years ago, intending to upgrade pretty soon after. I found an amp I love for $200? Yep. Now I know others here have felt that way many times, but this is the closest I ever came to a scroe (I hate that word).
Now, I really never was a Yamaha fanboy in the past (what's that Natural Sound mean anyway?), but they've been able to keep the doors open when so many others couldn't that they wore me down, I guess.
