1.76 in total? for all eight drivers getting 300 watts more each?
His drivers are basically co-located. He is running eight drivers of one CV-5000 watt amp - with four on each channel at combined two ohm load giving them each 625 watts (assuming the amp is putting out the full 2500)
When I read carp's question I was roughly thinking he'd get 1.5 out of 1 (using the generic formual of 50% increase of power gives 1.5dB, doubling = 3 db)
an additional 1.5 out of the second one (2 subs)
an additional 1.5 out of the next two (4 subs)
and an additional 1.5 out of the remaining four (total of 8 subs)
so my thought was 1.5 + 1.5 + 1.5 + 1.5 = 6dB more possible headroom for the whole eight drivers getting 300 more watts each --- ASSUMING THEY CAN HANDLE THE POWER -- because they are only rated at 600 watts.
6dB might be worth it if carp is crazy enough to want more. His house is ready to start imploding now - On the THX Amazing Life Demo I kid you not when I say the projector image looked like it was on some sort of pogo spring shining up to the middle of the ceiling and about 1/3 of the way into the room on the floor. This occurring on an projector that is VERY securely mounted. So securely that it knocked me to the ground when I hit my head on it during one visit. So I don't have any idea why he'd want more.
The bass is nearly becoming painful. As I was driving home last night I felt like I'd been worked over.
But at any rate - regardless of how enthusiastic you are for bass I think most would agree that if it is truly only a 1.76dB gain for 8 subs getting 50% more power - then I'd pocket the $650 the extra amp costs instead.