@bigkidz is right. Get a tech to inspect the schematic and identify the most critical resistors and capactors (typically the input resistors and the gain resistors), and upgrade those to the best you can afford. I use nude Vishay resistors, which are incredibly good, and incredibly fragile.
For caps I use film and foil MIT styrene caps, which are relatively neutral to my ears. Polyproylene can be warm and fuzzy, teflon can be hard and cold. Best of all are vacuum or air dielectric, but they are impractical for an upgrade.
For caps I use film and foil MIT styrene caps, which are relatively neutral to my ears. Polyproylene can be warm and fuzzy, teflon can be hard and cold. Best of all are vacuum or air dielectric, but they are impractical for an upgrade.