FWIW, as I do not own PL7's. I have a PL3 and a PL5. The PL 5 without the PL3 in front of it is enimic. With it it has credible bass, if not amazing. You can read about this in the 6moons review. Other preamps used were ARC SP10, Magus A2, and EAR 834L. I also noted in a review in the big mags that they thought the PL3 was synergistic with the 7's although they seemed to fault the output impedence of the PL3. Seems counter intuitive to me but I didn't spend much time thinking about it.
Now to the extent that that situation exists with the 7's matched to another preamp, I don't know. But be cautious.
Now to the extent that that situation exists with the 7's matched to another preamp, I don't know. But be cautious.