This has been an interesting thread! With all that math being thrown about, I was about to call for an RMA on my ADA1500 because clearly the difference I thought I heard was all in my head!
Not really...
But to get back a little bit to the original question that started all this, would it be better to upgrade the OP's sub-woofer or get a new amp?
I originally based my answer on what I heard when I added an ADA 1500 to my receiver and it made a very big difference -- much more than I expected! The OP was in a similar situation to me, with M80's and a similar receiver but a 'cheapish' subwoofer.
I can say that I often like to listen to music quite loud, and this is certainly part of the difference that I heard. I checked the owner's manual for my receiver and it claims 125 Wpc @ 8 ohms for all channels, without specifying how many channels it can really drive to this level. It also claims 'Dynamic Power' up to 170 Wpc @ 8 ohms or 270 Wpc @ 4 ohms for only two channels driven. Either way, the ADA can no doubt produce much more real power when driving my M80's!
However I don't think that is the full story, as the ADA seems to sound better even at lower volume levels, though it is not so noticeable then. I do think that the difference is not only in the bass but across all frequencies.
Now let us ask a different question: How much better would an upgraded subwoofer sound? I don't know from direct experience but it does seem to depend a bit on what the system is used to listen to and how the listener likes it to sound.
I've been trying for a fairly neutral, clear sound, which I think the Axioms largely deliver regardless of amplification options. I myself don't have a very good subwoofer, so when I set it up to blend in well with my system, it probably can't go much lower than the main speakers (M80's or LFR's) can go on their own.
After all, the M80's can produce bass down to around 30 Hz or so. My sub is only rated down to 20 Hz and at that point I think it is already down by 9 db or so. The M80's themselves are probably only down by 12-15 db at 20 Hz. So assuming the M80's are being driven full range, with my sub I may only really get a slight emphasis in the bass below 30 Hz. What's down there anyway?
In terms of music, there's not much other than tubas and pipe organs that can play below 30 Hz, and even then, when do they? I guess that a better sub might be able to reproduce better, lower explosions with more rumble, but that would only help with movies (mostly action movies) and perhaps the 1812 Overture, wouldn't it?
