I thought this new review of the Circle Labs P300 preamp ($7495 USD) + M200 stereo/mono power amp ($9995 USD) did a particularly good job communicating what these pieces are all about:
hifiknights.com

Circle Labs P300 M200
Circle Labs P300 M200 pre/amp combo delights the eyes and ears. Why? Find out from the review @HiFiKnights.com; a review by Marek Dyba