I own both units.
The DP-67 seems to have a bit more resolution, a bit more detailed and present high end, and a ever so slightly more defined soundstage. However, the DP-55V seems more musical to me. They both sound Accuphase and I think it really comes down to taste actually. The differences are not that great but very clear in a side to side comparison (I suspect it is because the DP-55V sounds a bit dark).
To A/B them, I put them through my Conrad Johnson PV11 preamp. However, my normal setup is straight out of the Accuphase DP-67 to my VTL Deluxe 300 amps. The DP-55V goes straight out to a Grado headphone amp to my Grado RS2 headphones I have sitting at my desk.
I am not sure which I like better.