I work in one of the UKs best HiFi R&D departments so I could answer this one!

People think higher voltage elec. caps sound better as they are meant to be more linear with change in voltage on their plates. Film is the best to use in this application. Use a large ECHU capacitor perhaps use two 470nF in parallel rated at 10V or 16V is absolutely fine.

Slightly off topic (curiousity has got the better of me)...the schematic you posted shows a bipolar supply, so why are they using a virtual ground IC in the power supply section?

There are parts of your schematic cutoff from view so maybe that the bit of the puzzle I'm missing!
If you mean R3 and R4 they form the global closed loop feedback.