Adding amps to standard Audi head unit - is this the best way?

My 1998 Audi has the standard Concert tape deck. I would like to retain it for the OEM look but add some amps and uprated speakers. As it can run a cd changer I plan to add an ipod adaptor, something like the xcar link as the music source.

I understand that this unit powers the Audi's front speakers with its own internal amp and has a low level rear output which drives some active speakers in the rear.

I would like to tap into the low level output and use it to feed a 4 channel amp which will run some Pioneer components front and rear, but I am going to need to use an Alpine 4312 dual amp signal balancer to split the single signal into two to feed the front and rear low level inputs on the amp (Alpine 3555). This is my chosen amp but it does not have high level inputs.

Does anyone know what voltage the low level output is likely to be on a unit like this or how I would even find out?

Also, would the Alpine balancer literally halve the signal into two outputs?

This is the head unit:


This is the Alpine balancer:


I figure at a later date I can still consider running a sub from the high level front outputs as my Alpine mono amp MRP-350 will accept them.

Any advice?

My main concern is the quality and level of the standard head units outputs. I think I am right in thinking the head unit was made by Blaupunkt so it can't be that bad?

Opinion?

Stu