Audio Research SP-9 Mk-III vs Audio Research SP-11


I have owned an Audio Research SP-9 Mk III for a short period of time and I love it. An SP-11 MK-2 is available for trade and cash. How much improvement will I experience if I upgraded to the SP-11 Mk-2?
My system:

Audio Research SP-9 Mk-III...............preamp
Sunfire Signature........................amplifier
Oracle Delphi Mk-I /Grado cartridge......turntable
Carver SDA/350...........................cd player
Infinity Kappa 9.........................speakers
Infinity Renaissance 90 ..................speakers

(I alternate the speakers periodically)

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A friend has owned MANY preamps including a large number
of the ARC preamps, SP-9 among them. He has had the
SP-11 MK II for several years, and considers it the best
ARC preamp ever made and one of the best preamps of
all time.
I owned and enjoyed my sp11 for many trouble free years.It all depends on what your looking for. I found the SP11 warm and a little forward, with forcefull but round bass. I did eventually move on to a more nuetral,refined tubed linestage (Thor) and I am not sorry I made the switch.If you like warm tube sound with a good bass line I think you'll love the Sp11. It is also built like a tank! Good luck