What is the best DAC under $3000

The Ayre QB-9 is a very good DAC in your budget.

there is no best anything in a price range. there are on compromises. if you want richness fin a dac with a sensitive tube circuit. I suggest you listen to many products in your price range. you will learn what is possible.

just a reference point, the mhdt products are nos dacs--rich, but lacking in bass. the modern tube dacs, which are oversampling, like the eastern electric, are extended , top and bottom, but lack liquidity and bloom.

DACs to consider are:

Wyred4Sound dac2 SE
Auralic vega
Benchmark DAC2
NAD M51

Start with Rega's stand alone DAC.
These can be had used for $650 or so.

I had an XA7, fine unit. PLATINUM has a unit that upsamples to DSD, not sure on price. I wish the new Sony HAP-Z1ES had a SPDIF, but it does not. If you can live without DSD upsample, the latest BRYSTON dac, and the NAD M51 are very strong choices. Your XA7(as long as the Saphire platter bearing isn't worn)is an excelent transport.