The Cary is listed at 15W per channel, although I checked with a lot Single-Ended designers on Audio Asylum and they say that while 15W may be possible w/ a 300B tube, at that point the tube is being pushed extemely far outside it's linear range. I guess that means while 15W is possible on paper, the resulting sound is horribly distorted. 8-10 watts was the general consensus for the maximum acceptable power from a single tube, and that is driving it flat out at that point.
Anyway, back to the point of 300B's driving Meadowlark speakers. It all depends on what type of music you listen to - excellent for chamber music, small scale jazz, acoustic, folk, etc. Not so good for rock, hard rock, metal, industrial, dance, rave, etc. The speakers are to require too much current to move complex passages with heavy bass, percussion, or low frequencies for extended periods.(more below)
As to what the combo did right, the Cary SEI and Kestrel HR's provided glorious midrange and high frequencies. Mids had a tonality and texture that gave me goose bumbs, especially on saxophone, vocals, piano, cello, etc. Nat King Cole, Sarah Vaughan, Fran Sinatra, Diana Krall, KD Lang, etc. all were rendered with such realistic texture and delicacy that at times I could a soft intake of air or their tongue moving in their mouths. In the lower regions of midrange, vocals were delivered with power and depth that was startling. And high frequencies had the most amazing "air" and space. It really filled the room with terrific spatial orientation. I was simply awestruck. (this was my first experience with SET sound)
Amzingly, low frequency were incredibly detailed and accurate as long as the musical section did not become too complex. I used a demo cd of traditional Japanese drummers that actually blew my mind. With a single drummer on the large tympani like drums, there was deep, textured resonance that blossomed like a live concert. I could clearly hear the difference between strikes near the edge and the center of the drum skin. And how the note resonated towards the center of the head. It was like the drummer was actually in the room with me.
On the downside, whenever more than one drummer was in action the amp quickly ran out of steam. It was like the bottom had fallen out of the music. Anything below low-midrange dropped off and sounded like it was in a shoebox. The same held true for rock and pop, if too many instruments got going the sound collapsed. I think they call it transformer saturation(?), whatever it is, it means that an amp only has so much reserve power for short burst of high power, and that it needs a period of time to recharge. If it does not receive a breather, than it is faced with diminishing current and bass requires the lionshare of power, so that is the first to go. And most of the time it was slightly flabby and out of focus, although some people have posted that this is a typical Cary problem. I have no idea whether it is true because that is the first Cary, and, SET amp I had ever heard.
But, Since then I have had the good fortune to hear quite a few other SET designs, both DIY and commercial, 2A3 to 300B, and I can tell you that I don't(my opinion) think the Cary is worth the $4,000+ they charge. There are so many other designs at far less than half the price, that deliver equal or greater performance(my opinion again).
Then again, in fairness to Cary, I should audition the amp again with much more efficient speakers before I spout my mouth off. Also, the dealer said that that particular amp did not have very amny hours on it, far below what was necessary for breakin(why would the have it out, then?).
As for the Meadowlark Hestrel HR's, I think they are an amazing sounding speaker. I had the opportunity to drive them with an Aragon 8008(?) and was delighted with many of it's traits. The most amazing thing was A/B'ing them against my Jean Marie Reynaud Twins mkII (monitors, $845) and how mouch tonal simialrity the two share. They could almost be models from the same line! Both provided excellent tonality, imaging, and detail, with the only major difference being the HR's slightly deeper bass(obviously, a floorstander). I would love to do a shootout between JMR's Cantabile floorstander and the Kesterl HR's - that would something to hear.
I suggest you check out Jean Marie Reynaud speakers if they are available near you. Definetly as good as Meadowlarks.