i see no reason that all items cannot be run from one battery - one could even go so far as to use DC/DC converters to create a small power brick of multiple DC outs. i have run a small mixer from a dc/dc converter powered by a pair of 6v SLA's (for 12v > DC/DC device) and then run a D8 from one of the 6v's and an HHb on the 12v tap with one of my digi-disto boxes on the 12v tap as well.
BUT one nice thing is that you can start using LiION batteries to replace SLA's. they come in all sorts of voltages and because they are so small and liteweight, one could haul two or three different voltages and still weigh less than one sla. that may make up for the "i'm so tired of lugging these d*mn SLA batteries around - one 12v, one 6v, blah blah" check the post after this one. i put up a ;ot of battery info.
btw, i use a LiION 14.8v to power my 671 and shure fp33 - lights on all the time, 48 phantom, headphones powered all the time - in place of a 7lb SLA. the LiION weighs 10z and runs 8hrs. and is smaller than a paperback. recharge in ~4hrs
neil in san marcos