Under 1k integrated recomendations

I agree the AR "The Complete" is a nice amp, as well as the Bryston. You could also look for a used YBA Integre for $1K or the Integre DT for slightly more. YBA is who makes The Complete. Also around $1K used is the Creek 5350R and 5350SE.

Definitely YBA Integre DT. Don't bother with the single transform version even though it is cheaper. It won't be enough power for the Concertinos. I've seen 3 DTs go in the 1100-1200 range in the last 4 months on audiogon and ebay so there are sellers.

And the bonus is if you get an Integre you will be so far up the hi-fi ladder you might find you don't need anything else.

Cyrus makes a bunch of different integrateds. Cyrus 3
with PSX power supply should be within $1000 used.
Audiolab 8000S would go quite well.
Densen B100 (I own) is a great little amp, slightly less
powerful than the previous two, but perhaps a bit more
detailed.
Newer Arcam models seem to get glowing reviews, but I haven't heard them myself.
Of the above I think there's a few currently for sale on
Agon.

I hate to introduce budget tilt but there is an Audiomat Arpege (integrated tube EL34) for sale here for $1250 and it's a wonderful amp. Might buy it myself. Take a look

Sincerely, I remain

As others have previously mentioned, the Bryston BP-60 is an excellent choice that will mate well with many speakers and comes with a 20 year transferrable warranty. I personally have always been impressed with Creek integrated amplifiers, their phono sections are unbelieveable for the price, and their are many available on Audiogon for less than your budget. There are some great deals available from a number of retailers on Anthem integrated amplifiers that may be the best bang for the buck out there now. Good luck.