Give it the "G3153B1 (scroll down)
" -- just be prepared to change it every hour.
To give you an idea, I use a self-made modified CHA-47, and it's getting about 34V right now off a regulated power supply I just finished building. An extra 0.6V is well within the engineering tolerances of that design, I assure you. The main concern would be the rail splitting mechanism taking more power than you want for the battery life (not a concern for me) or the LED getting too much power (I'm not sure what resistor value they use) but neither of those are very big deals when going from 9V to 9.6V -- anyway, you'd be surprised what kind of tolerance actual batteries have on their voltage. It isn't pretty, and in cases such as powering opamps, it doesn't have to be.
To give you an idea -- I just turned the power supply I'm using down to 2.4V volts TOTAL and it sounded ok, and any lower than 2V it was clipped and distorted. That's +1.2V and -1.2V using AD823 opamps giving me fine performance. Then I cranked it to 34V again where it really shines -- and this works because I know my LED-resistor chain can handle it, and my opamps are good for it. 9.0 to 9.6 volts is nothing in this setting -- I don't know if you'd hear much of any difference, but you may have better ears than I do. I'd say what you are really looking for in batteries is a low price/mAh ratio -- you want to run your amp for a long time without changing batteries, but you don't want to pay twice as much for an extra 40 mAh. I'd suggest not even paying more for an extra volt because I really don't believe you'd notice the difference between 8.6V and 9.6V, particularly when batteries are anywhere below, above, and all around their nominal values.