What Power Cord for EAR 834P

Will a power cord on this phono stage make much difference?

Abruce, a good PC on ANY highly-transparent phono stage can make a difference! Just the potential lowering of the noisefloor will yield benefits of increased delicacy of detail, and hence perceived improvement of so-called "microdynamics". If you get a better one using a great dielectric like Teflon then you'll also benefit from less phase "smearing" from dielectric absorption and rebound.
I have found that the industrial Belden 83802 12AWG in all-Teflon in such a cable, and assemble easy DIY Kits comprising this magical cable and great connectors. Best of all, it's only $35. Sorry to plug here. Ernie 781 483-3922
I would give Bill Parish (GTT Audio) a call. He's an EAR dealer and also markets the Absolute Power Cord. The Absolute is an inexpensive, well made and properly tuned power cord suitable for line level components.
BMI Shark
I got a bit more body in the sound when I replaced the stock power cord with a Delta Labs PC on my EAR 834P. You will realize a more dramatic improvement if you upgrade the tubes. I am using NOS Mazda 12AX7s. Other 12AX7s with good reputations are the GE 5751-WA Black Plate, the Sylvania black plate & Gold Brand black plate and and the Sylvania Gold Brand grey plate gold pin.