2000 Gain Preamp circuit 20Hz/20kHz help?

If you look at the top of the General Electronics forum, there's a 'sticky' about just that!.

Adding simple filters in series causes a droop in the frequency response before the cutoff, no sharp corner at cutoff.
An active filter uses an opamp to sharpen the cutoff corner, a Butterworth response has a sharp cutoff corner and a flat response before the corner.
An active second order Butterworth filter is twice as good as a single RC filter and higher orders are even better as shown here: