In addition, generally speaking I would not expect a full-function 2.1 channel preamp + DAC + headphone amp costing $1495 to provide particularly good noise performance in its built-in phono stage.
Also, FWIW, I use a Herron VTPH-2 (not 2A) in conjunction with an AT-ART9 LOMC cartridge rated at 0.5 mv, with the Herron’s stock tubes. If I turn the volume control in my system to a setting slightly higher than I would ever use (which is quite loud; some classical symphonic recordings I listen to can produce 105 db peaks at my 12 foot listening distance) the hiss produced by the phono stage is only audible within about 1 foot of the speakers. The Herron (which is only a phono stage, not a line stage or preamp) provides 64 db of gain and lists for $3650.
In addition to the SUT approach that was mentioned, a number of separate phono stages are available which cost considerably less than the Herron and have received a lot of favorable commentary here and elsewhere. The Gold Note PH-10 being one example. I believe that using a quality external phono stage connected to a line-level input of your P6 would considerably improve both the hiss and the sonics that you experience when playing records.
Good luck. Regards,
-- Al