Transforming a 300W Sinewave DC/AC Mini Inverter to a 5000W Monster

I was planning to build a PIC microcontroller sinewave inverter and while browsing the internet to buy the necessary items I got accross this little 300w ready made pure sinewave inverter which would cost less than all the main items I was searching.
An idea flashed in my head to try to drive my "already have" square wave inverter's power stage from this ready made thing so I went ahead and ordered it.
After receiving the item I ran some tests on it and was surprised of the many hidden options this tiny thing packed:
-Built-in PWM maintaing a stable 230v at all times.
-Over voltage "+15v" and under voltage "+11v" cutoff.
-Low battery audibale warning.
-Overload cutoff
-Waveform distortion :<5%

Actually 300w is way too much to drive the power stage, 100w would have been more than enough and the price would be much less but unfortunately I didn't find one.

Anyway.. The idea was a 100% success, I connected the mini inverter to my power stage that I already have built from a previous instructable and the monster came to life just as was expected :)

Of course you can adjust the power stage to your needs following the table of my main instructable.