Well I’m going to have to drag home one of these $4-6k DAC’s, because right now I’m listening to Cowboy Junkies, “The Trinity Sessions” through my RME ADI 2fs with Teddy Pardo LPS, Nordost Frey 2 Balance direct to Cary V12, Frey 2 speaker cables finally to Wilson WP 6’s and I can’t image without upgrading speakers it could get much better. I’m sure the big dollar DAC’s are better but I’m not too worried about it.
Before I would dish out big bucks on a DAC, I’d look at a streamer over using a computer. Never used a PC admittedly so I could be missing something. I have owned Kimber 8TC and a couple PK10 Golds and they are good cables, but not the last word in resolution, air and speed. I’d experiment with other cables first before you toss your Pro Ject to the curb. If the Pro Ject uses a SMPS maybe spend $400 and get a good LPS like a Teddy Pardo.
I don’t know your Pass but own a X250. I’m sure your INT 25 is wonderful with your SF which I have heard. Thinking that combo is great. I’d suggest a cable upgrade, a linear power supply on your DAC if it’s a switched type and for starters try the current Node as a streamer.
Good luck.