ARC D-115: What tubes and cables?


Hello all, I am seeking input on which tubes and cables will help in providing neutrality and extension in the highs for this amp. The tube complement is SED 6550 with 50% life in them and brand new Gold Lion and Sylvania NOS for the driver tubes. My dealer suggests KT88s slhould be next.
Any input would be appreciated!
128x128wahwah
Thanks guys, this is the first tube amp that I've owned.
Prior to this, I was using an ARC D-120 that simply got out
of the way and made my Proacs really sing.
However this is an entirely different beast! (LOL)
I always used 6550 tubes from ARC with this amp.
In your header you also ask about cables.
I found Purist Audio to work extremely well
Goldeneraguy, I was using Radio Shack 18ga solid core cabling with the D-120. (No kidding). So Purist seems like a gigantic leap. Any other sugestions?
I'm using SED 6550's which are a great tube in my D70Mk2. Also using a pair of Nordost Red Dawn 2's...very quick and open/transparent cable. If you can source a set of GE 6550's, they would also be a great match. BTW, KT120's will NOT work in the D series amps.
Wahwah ,Yes Purist wires would be a giant leap ahead.
Magnan worked well at a more reasonable cost
Without knowing your complete system its difficult to suggest what should work for you but I would upgrade the Radio Shack wires before replacing the tubes