I know I have heard of diode biasing, and its great if you want to control the system, but this is a raw power amp, the longer it loops....the higher the output.
so use a 9v...wow thats a lot of power man! so if you loop it say... 5 times... thats like 45v! so you want some monsters in there... nothing under 50v will do if you want lots of sound. now about that 8ohm speaker.... even a 7 watt system sounds better with 8ohm speakers, most are only 2ohms. but with 9v... well you get the picture.so take that 10% rule and don't mess with the output. Because.. you aren't system matching, your pumping out the jams. get fets!!! and think 2 phase..
My solution to building amps was to think like an egyptian... they built 4 sided pyramids(the true pyramid has 3 sides) Where you might connect an input with a small cap you really don't need it and at the output, the power must be enough to drive the speaker. not enough power and you won't have an amp you will have a compressor of sorts. The idea is... load a slow cap with a charge, and while its loading, load a transistor with the same charge. When the cap fires, it triggers the transisitor, and drives the combined charge(double the signal) onto the next phase, which loops the current with the help of some resistors.... when the resistors can't resist anymore, they drive the speaker. raw power use is very very shocking sometimes!