Audio Research SP8 MK II Sounds


Just bought an ARC SP8 on ebay and installed it in my system. Vocals sound boxy and a bit too forward to me compared to my McIntosh C20 preamp.
The SP8 was sent to ARC recently for a checkup, new tubes, were installed, etc....
The tubes provided by ARC are Electro-Harmonix, but the tubes in the Mac are Amprex Bugle Boy and Telefunken. Could this be the problem? Don't really want to spend the money for more expensive tubes if it will not rectify the problem.

My system:

Krell FPB 300cx amp
ARC SP8 MKII
Wadia 861 CD player
Mac MR78 tuner
B&W Nautilus 800 speakers

New to Audiogon and was also wondering how to contact other audiophiles in my area (South Florida)?

amaka
I think Reylon meant to say E88cc for the 6922. The E83cc or Ecc83 is a 12ax7. Speaking of Mullard 12ax7, the best, although rarer and expensive is a late 50's long plate, square getter( magical sound in the right circuit) Also, find an early pair of Siemens Cca( lower noise version of their E88cc,6922).
I have owned an SP8 for some years and am very familiar with the C-20 Mac. There is no way the SP8 is forward or boxy. It is extremely airy, rich and musical. The C-20 just does not compare. My guess is the Krell may have too low of an input impedance and loads down the SP8. Many high dollar tube preamps, like the SP8, do not work well with all solid state amps. The Sp8 is one of the best preamps ARC has produced and it exudes listenability. Voices are really special and real sounding. The phono section which is a moving magnet and quite good.
One other thought is that 861 is a little to clinical and solid state sounding in it's stock form. The Great Northern Sound mods transform it, making it warmer, smoother and richer sounding.