I run my Metro IIIs with 40wpc of PP KT90s strapped in triode. Room size is 16" x 20". I don't feel the need for any more power, and I do turn it up now and then. Really, because the soundstage is so robust, I don't often feel the need to. I've also connected a number of EL34 amps, 30-40wpc, and was quite happy. I know of one user with Metro IIs that found ultimate happiness with an Ayon Triton, but I believe he has a larger room than mine.