Some background ... I am using the PL2 with Ascend Acoustic Sierra 1s and a Rega Apollo CD player. The interconnects are Audioquest Black Mamba II and the speaker cables are QED Silver Anniversary. I have tube rolled a bit over the 7 years that I have owned the PL2. For most of that time, I have used EL34s or 6CA7s and always new production Electro Harmonix and Mullard or Tung-sol reissues.
My primary reason for purchasing the Sierras was that they are equally at home being placed vertically or horizontally on shelves, which is a constraint in my set-up.
With all that out of the way ...
I have tried a number of monitors with the PL2. Some were consistently very good to excellent (Rega Aras and Omega Super 3i), some were good most of the time (Energy RC10 and NHT Super Two), and some were just average (Spendor SA1 and Totem Mites). None of this is meant as a judgment on these speakers, but rather how the speakers performed in the way that I have used them.
The Sierras sound very full. Bass goes pretty low ... not boomy at all. Good amount of detail, without an overemphasis on the detail. I can listen to these speakers for hours on end. I can not speak to things like stereo separation, mostly due to how I have the speakers set-up (on their sides, on top of bookcases). Overall, I am very pleased with the Sierras and have been using them for a year now.
Rich