But ... they only want signals up to 5Khz, which is bugger all. So you could oversample (even a stock audio chip will do 96Khz) then apply a low pass filter wit

But ... they only want signals up to 5Khz, which is bugger all. So you could oversample (even a stock audio chip will do 96Khz) then apply a low pass filter with an FIR. Why wouldn't this work?