I'm jumping in 8 months late here, but since I have a pair of Firebirds, I thought I'd offer my two cents. The Firebirds do indeed have loads of very fast and accurate bass. However, without having heard the Avalons, I can make a few comparisons that might still prove helpful if you're still in the market.
The Firebirds are an easy load at 90db sensitivity and a nominal 8 Ohms (not dipping below 6 ohms). The diamond tweeter is a straight drop-in for the stock ceramic, so can be added later to make the entry price a good bit easier to take. Plus, the Firebirds really are a work of art, not just a piece of audio furniture. That's not to belittle the great look and quality of the Avalons, but the Firebirds have that folded wing bird-of-prey look that appears poised for action. We've actually had guests at the house who thought they were placed as an artistic statement, not realizing they were audio speakers. Mine are metalic black. Of course they really deliver the goods, musically. In all respects, I can recommend them without reservation.
I've been considering posting a full review of the Firebirds both here and on AA for some time now, and will likely do so within the next month or two.