If you've got the filter in hardware, then you can simply take sample 1 as the first sample, sample (5+6)/2 as the second, sample 11 as the third, ... (So you're picking a sample every 1/8Khz, and compensating for the fact that you've not got an exact sample at sample 5.5) To play back, linear interpolation is probably not too bad. If you can record at 8.8Khz, then just ignore the above, and use every 5th sample.