Two tiers in order to achieve the lowest ESR - top is using 4700uF and bottom, 15,000uF. Total around 0.8F, 25V.
I plan to try this out first with my TDA8566 but that's limited to 18V so if that sounds promising I'll look for a new chip which can handle the full 25V supply capability.
Update1 : Wired the top tier only underneath my new TPA3116 class D amp board from Taobao. Seems here the dynamics aren't limited by the capacitance on the output stage supply, rather on the analog supply (pin17 of the TPA3116) which goes to an internal LDO regulator. No amount of capacitance on this pin (I went up to 100,000uF) gives the chip the LF dynamics of my class AB amp so I've been off in search of a class D chip which doesn't have an internal reg so might be amenable to a hexacap on its supply...
Update2 - NXP's TDA8932 is on order now - this is a chip which can be DIYed because its in a manageably small SO32 package, so no need to order up an eval board. Over...