I owned the A21+ and liked it. I found it a bit warm, so I used the low-cost neutral Benchmark LA4 preamp with it and thought it was a great combo. They have a 30-day home trial.
If you want a bit more warmth than the LA4, then my other preamp, the Holo Audio Serene would work nicely with the A21+. I use the Serene today with the CODA #16, which shares some sonic character with the A21+.
My third preamp is also rather good but very warm sounding and has no remote control. It is the new Class A Schitt Mjolnir v3. I like my other 2 preamps more, but the Mjolnir is surprisingly good.
All 3 suggestions can be found from $1300-$3300.