How loud will 2 watts play? I easily get average 85dB and peaks of 95 with my 1.8 watt amp and 4 Pi Pros w/o a pre-amp. 12x18 room. There is lttle 'headroom', of course, i.e., rock bands will play loud but full orchestras will stress and clip the amp.

The 2 Pis have a lot of 'apparent' bass so I wouldn't worry about that. They're also a bit on the warm side with less detail than you get with better drivers. This makes them a good candidate for one of the inexpensive chip amps, at least until your experience grows.

I personally think the ST-70 is waaay over-rated. Depending on your budget, the Audio Note Kits 6550 amp would be great or build the JE Labs 300B, schematics and pix of the wiring are everywhere. I'm not familiar with the Decware or BH Sex amp.

I built one of these a few years ago and it blew away an ST-70 I had at the same time: Ella on Audiogon