how sensitive to ripple and noise in the psu is the amp9?
my last option for 24v, is an old military 500w dc-dc supply: ebay military dcdc psu
But I am a bit worried about how clean it is, since military radio equipment isn't exactly known for hifi
If this is unusable I guess I will try and run it directly from the battery and see if that is enough for my use. And if thats too weak I guess the only option is building my own smps as described in the amp2 thread, but I am a bit intimidated, so this converter is tempting if you guys think it will work.