I had a PS Audio DL3 Cullen lvl 3 and still remember that I really enjoyed it when I had it. I would say at the current $500 mark, new DACs will not be as enjoyable as it. You might get better measurements but there's no free lunch when it comes to budget components. I'd suggest saving a little bit more and getting something a little over the $1k range like a used Yggdrasil or Pontus II. Those should provide some technical improvements without losing musicality.
Dac: Old vs New
I have older DAC's that sound good but I've had them for several years. Benchmark DAC 1 and PS Audio Digital Link III with Mods. Would a newer DAC from, Topping (DX-5), Schiit (Modi Multibit 2)or SMSL, be a SIGNIFICANT improvement in sound? Seems like the newer DAC's have way more resolution and transparency. I prefer those attributes in gear over warmth.