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
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)?

Maybe its not a tube issue but maybe a wire issue,.I wouldn't think the same wires for Mac and Audio Research would be appropriate..Two different voicings...If you are using very analitcal wires on Mac and use the same on A/R you maybe need a more layback and warmer ( more full bodied ) cable with the Audio Research sp8...I would consider trying a few cables from the Cable company that might fit your issues...Cardas cables maybe.......
I had an SP8 for almost 20 years.The choice of tubes is important.It is a glorified Dynaco PAS III,actually,and it will never sound transparent.Try Mullards for the 12AX7s,and Siemens E83CCs for the 6922s.I tried many many different tubes-and those worked best.I had the MK. IV.
Click on Discussion Forums from the home page and scroll down to audio clubs. You might find something in Florida. Or try audioasylum.
Thanks for all the helpful tips. It is time for some experimenting with different cables and tubes! I will let you know how things work out.
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.
Amaka -
I live in the Tampa/St. Petersburg area.

Where are you located?
I'm in West Palm Beach.
Audio Research and Krell are mis matched
First thing, get a lot of hours on those tubes before you make a decision. I think EH tubes are harsh and unlistenable for at least, and I mean AT LEAST 50 hours. Then come back and maybe start tinkering.
Also, I'd hate to agree, but Augustusjohn might have something. Both of those pieces are fantastic in their own way, but they may not be the best match. I'll check that tonight.
Were you happy with the C20? Because if you were close to what you wanted with the C20, I'd say you're on the right track with the sp8. I just love the ecc88 difference, it just blooms! What cables and XLR adapters are you using with it? I lean towards silver with the sp8.
Myself, I'd be deathly afraid of blowing amp/speakers up with the ARC's questionable mute delay!!!! I know, I've done it.
Also, I'll agree that the tubes make the biggest difference with the preamp. I'm using telefunken ecc83's and ecc88's. And it does not sound boxy in the slightest. I'll hook mine up to my fpb600 tonight to see if I get anything like what you are talking about. I usually use the sp8 in my analog/phongraph system with a d75a amp and silverline sonatas and rel strata sub, synergistic connections.
The krell is with reference one sometimes, but mostly directly from the dac/computer to wharfedale opus 2's which are a little similar to the nautilus design, except for the dome/cone midrange, which I think makes the nautilus a little dry and woody compared.
Whatever you do, Don't be like me, and make a rash decision until you give it some time. And get rid of those EH tubes!
I am an authorized repair station for ARC and a past owner of an SP-6B. I have also owned a McIntosh C-20. They are very different sounding preamps. The C-20 uses a tube rectifier and so the bass can be a bit soft. The top end of the C-20 can also be a bit soft due to circuits like tone controls and a limited frequency response etc. It does not have a flat frequency response. The SP-8 uses a tube regulator in its power supply. It has a much better regulated power supply in it then the C-20 which has virtually no regulation at all. It has a flat frequency response. Both preamps high level stages are similar. The phone stage is a bit different. The SP8 should sound more open, have better bass and have better top end, as well as lower noise. It's possible the preamp needs to be recapped and your regulated voltages are wrong. There's no need to update this unit, which I have done in the past, without first checking to see if the power supplies are running properly.
Tried it for a couple of days with the fpb600. Not the best, but not bad either. But I was wasting the amp with the single ended input. I think a little darker than it should be.
After thinking about it. Why did you get the sp8 (or even the mcintosh) if you're not using a turntable with it?
Strange pick of preamps, considering the rest of your set-up. I would think something more modern would work better with your rig. Good luck finding it though...