Tube DAC, be gentle first time

I am thinking of adding a DAC to my system. I would like it to be a tube DAC since I have over the years been going back to an all tube system. I will be streaming from my Sonos to a Cary SLP98 feeding a CJ MV60SE. I need to keep the budget under $1000, and it would be better if closer to $500 for this first time purchase. I would like to buy used.
Questions:
Is this an upgrade or just a sideways move at this price range?

Any product recommendations, please be a specific as possible?

Thanks,
Doug