Integrated with Excellent Phono Stage

I am looking for a SS integrated or even a vintage receiver for my son. He has a pair of PSB Stratus Minis and one of the Lenco turntables that he helped me build, along with a pedestrian Pioneer CDP.

Looking for piece for about $500-600 USED that would match well, and having the best phono stage possible. It has been so long since I was in the integrated arena that the whole current lineup has passed me by.
You might want to consider the Pioneer SX-1250 Receiver. Before I purchased a SX-1980, I used the SX-1250 and IMO it had a very good phono stage as well as better than average tuner section. I paired it with a Nottingham SE turntable/Rega 250 arm (modified)/clearaudio beta/s aurum cartridge - outstanding sound at the price level that you mention.
The older Musical Fidelity integrated (the original A1 and A100, sold in the U.S. under the British Fidelity name) were excellent sounding amps and had great sounding phono stages. I believe Tim DaParavinci was the designer. The Advent receiver also had a very good phono stage. The Advent can be had under $250 and can be readily found, the Musical Fidelity amps are somewhat rare in the U.S.

Also, any late 70s thru 80s Luxman, Marantz, Nakamichi, Tandberg or Yamaha receiver will have reasonable quality, if not the equal of those in the first paragraph, phono stages
I'd look for a musical fidelity A3. Great integrated, and a decent phono stage. Can be had for about 600 bucks.
used Tandberg int amp might work...very nice units with exc power and plenty of inputs
vintage ss mac receiver or integrated. they not only sound great, you get a history lesson to boot