6sn7 and 5u4 tubes

Yes, especially the 6SN7s. The Sylvanis seem to be a great match for Cary gear. I'd do those first and see how you like it. There is definitely a difference between the stock tubes and NOS.

If you can find some CV1988 Brimars....one of the best usually go for around 100 a piece.

A good place to start would be to find a NOS pair of Sylvania or Ken-Rad VT-231 bottom getters from the 40's. That's IF you enjoy a very accurate and transparent presentation. This is what to look for: (http://cgi.ebay.com/Pair-Sylvania-6SN7-GT-VT-231-Preamp-tubes_W0QQitemZ170271128352QQcmdZViewItem?hash=item170271128352&_trkparms=72%3A570%7C39%3A1%7C66%3A2%7C65%3A12%7C240%3A1318&_trksid=p3286.c0.m14) (http://cgi.ebay.com/Ken-Rad-Vt-231-6sn7-1940s-Matched-Pair_W0QQitemZ220293427549QQcmdZViewItem?hash=item220293427549&_trkparms=72%3A1205%7C39%3A1%7C66%3A2%7C65%3A12%7C240%3A1318&_trksid=p3286.c0.m14)The top getter Sylvania "Bad Boys" don't even compare(EXCEPT for the 6SN7W/JAN CHS, tall bottle). If you like a "warmer"(British- Brimar/Mullard) coloration: Try RCA, Raytheon or National Union VT-231's(again- bottom getters) from the same era. They all deliver great timbre, tone, frequency extention, wonderful soundstage and imaging(if the rest of the system/room is up to it. I've never purchased from those sellers on eBay, so- I can't vouch for them.