I've used a First Watt F6 clone (50 watts into 4 ohms) with my Spatial M4's (not the TM version) for a few years. I preferred this over my previous class D amplifier, which put out over 300 watts, if I remember right. I went ever further down in wattage this past week and rebuilt the F6 into a First Watt Aleph J (13 watts into 4 ohms). It's been a short period, so far, but there is more than enough, of quality sound.
With any of my First Watt experience, I don't feel like anything is lacking, and I really like them paired with the Spatials. With that said, I do have an open baffle GR Research/Rythmik subwoofer paired with them, since that has it's own amplifier, it likely picks up any slack on the bottom end.