Bass Amplifier made from cheap Aura InteractorAmplifier

This is my Firs Instrucion, so the next ones will be better ;-)
I have bought an Cheap (5Euros) AuraInteractorAmplifier from a german Shop
http://www.pollin.de/shop/shop.php?cf=detail.php&pg=NQ==&a=NTk4OTYzOTk=
It delivers approx. 16W RMS.
The Powesupply primary is 220V...240V at 50Hz.
They wrote you cold use it as Subwoofer Amplifier, but when I tried it, the sound was horrible.
So I modded it with good results.
Sorry, not much fotos since i have lost the data cable for my mobile phone :-(

Step 1 Overview

Here is the original plan before my changes. You see a lot of things needed for a buttkicker, but not for a (Sub)woofer driver, like the flipflops U3 and the multiplexer U4, they are ripped off by me.
The cutoff frequency of the lowpass filter, it is a sallen-key filter of 2nd order, is too high, so it has to be changed. All coupling condensators are too small to get a good bass response so they has tobe changed.
There are some other useless parts, but they can stay on the board since they do not disturb the sound.