My processor is a AudioControl DQL-8
It's an 8 channel line output converter and EQ. The Inputs on the DQL-8 must be High Level which means they come after Bose Amp from the speaker level outputs and sums all the signals together including the high speaker level outputs from the Bose Sub amp. It's probably still not as full of a range as it could be if it was connected directly to the Headunit but it gets the job done, and its crips, clear, and loud and plenty of bass.
What ever you do don't try to connect a LOC from the Low Level signal. The LOC works best when you input from Speaker Level and convert to RCA.
If you take a Low Level signal with a LOC that accepts High Level the volume is going to be really really low and you won't be happy especially with the engine noise that will be introduced.
In order to do as I mentioned with Tapping into the signal before the Bose amp you'll be taking from a Low Voltage signal, I believe its 1.5V. By tapping into the wire and leaving it connected for the shield part to continue doing its think and cancelling out the engine noise you'll need to making your own RCA cable. So from that you could try connecting directly to your amp and see if accepts it. If it works and no noise introduced I would consider buying something like this to boost the voltage if your on a budget:
3SIXTY Analog Processors - RF-BLD - Rockford Fosgate®
If you have cash to spend you could go with the new 3Sixty.3. It looks pretty nice and accepts balanced inputs.
3SIXTY Digital Processors - 3SIXTY.3 - Rockford Fosgate®
Like I said before, I don't know much about the balanced outputs, but from what I've read up on them, our Bose system works very much like an XLR balanced connection. So I really don't know how amps like +1.5V and -1.5V and if it will even work. So do it at your own risk.
To give you an idea what a balance vs. unbalanced is here's a diagram:
Which means this:
+1.5V Signal
-1.5V Signal
- Shield Cable
There are two alternating signals -1.5v & +1.5v and the shield. The advantage of this connection is the noise (interference) is canceled out. The downside is once you disconnect the shield cable it introduces some horrible engine noise.
Here's a diagram I made that might help you if you choose to go this route.
If you don't feel like being a guinea pig you an go the safe route and do what i did. Just get a summing device. You can go with something as inexpensive as RE-Q5 which is around $150.00 or spend some bucks and get a $500-$700 summing and EQ device. I'd recommend getting something with an EQ so you can try to correct some the bastardization the Bose amp does to the signal.