I think you're set for the sub. Jim's probably forgotten more about budget subs than many of us will ever know.
As far as the amp goes, that depends on your usage and expectations. Is the system for desktop listening or are you wanting to listen from the other side of the room? Do you like to crank it up or stick to more sedate levels? [Rock & metal... I think I know the answer.
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So you know what the additional power will do for you...
The SA-50, based on the 50WPC spec will theoretically play each Mica (85dB/1W/1m sensitivity) to 92dBSPL @ 1m. Add the contribution of a second speaker and a sub all playing together and you're up to around 97dBSPL @ 1m. Quite loud.
The TP-21, with it's 25WPC spec will theoretically play the Mica's at 89dBSPL @ 1m. The 3dBSPL difference is readily distinguishable as being softer, but not by what you'd call a significant amount. Again, three coherent sources and you're looking at around 94dBSPL @ 1m.
Bottom line though... if you regularly like to crank it up it's hard not to favour a more powerful amp, especially for a similar price. GranteedEV seems impressed with his SA-50:
Techtalk | SMSL SA-50 amp?, so that's good enough for me.
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