Hi Ausrock:
The difference between the Hafler and the Alesis is exactly how pipeline classified it: the Alesis is thinner sounding ... since I have a problem common to home recordists in getting bass to translate thru my 8" cone monitors (mine are Event 20/20s), I chalked it up to the monitors being what they are and my room being what it is. However, it seems this Hafler does a much better job at translating those: I don't know whether that means it's "hyped" or whether the Alesis was "scooped" in the lows.
As far as improvements over the RA 100 for new Alesis, I haven't a clue; I DO know
the RA-150 is NOT as powerful watts into ohms wise; but then again the Hafler P1500 is rated at lower power and yet it is clearer and has much louder output (I can crank the Alesis nearly all the way and not get intimidated by the decibels -- I'm a sensitive girl -- and yet I couldn't approach that on the 1500). So, it may be that Alesis gave their newer amps better translation, efficiency, signal-to-noise, and/or THD ratings. It may be useless to compare Hafler's specs with Alesis, but you'd think comparing an Alesis to an Alesis would be more like apples to apples. I believe they have manuals for all the amps on their Web site.
As you can imagine, my limited emperical data means I also have no idea how
the P1000 and P1500 compare. I sure wish I had found that guy's ad earlier ... I would've bought the P3000 in a heartbeat. Still, I'd say
the P1500 is definitely not lacking in power or clarity in my limited experience.