PSB Guy -
The M901 is rated at 87 watts into 4 ohms. The SongBird is an 8 ohm speaker. So it will draw less power - perhaps half as much. If you were using a 43 watt tube amp, I would say that is plenty of power. But this amp is not tube-based and it seems to me that this combination might be cutting it too close. The SongBird's are about 84db sensitive and I would opt for more power than that. You may be able to get away with it, but the SongBird's play quite deep for a single 5" driver and that takes power. I'm just not sure it would be a good combination.
The SongTower's, on the other hand, are 88db sensitive and a 4 ohm design. They would likely work quite well with that amp.
If it were me, I would opt for SongTowers to be on the safe side.
I hope this helps.
- Jim