Maybe you'd be better off with an R2R network as a Digital to Analog Converter.

Something like what Steven Wright did here (Not PBP).
SDMMCWavPlayer
http://www.sfcompiler.co.uk/wiki/pmw...SDMMCWavPlayer


And no, you won't need to save STATUS, WREG and BSR, unless you start using Low Priority interrupts.
The Shadow registers automatically save and restore them in hardware for High priority ints on 18F's.
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