Preamp upgrade or new preamp?

Using a Cary SLP-05 driving PassLabs XA-60s into Goldenear Triton One loudspeakers. I was considering the Cary Ultimate Upgrade ($1600) which supposedly boosts the preamp above the $10k class. Could I achieve better sound by selling preamp (approx 4.5k) and buying a used tube preamp for about $6k? I like the Cary cinema bypass mode and balanced inputs & outputs.
If you like the sound of the Cary but just want improved SQ I would upgrade the Cary for $1600.00. I would imagine the Cary and Pass sound very good together.
The upgrade is a bargain. I had mine done by Cary and it was noticeable improvement.
Thank you Iwin and Technik. I am now leaning toward the upgrade - probably in June.