After searching and reading through some threads, I see that using the low level line out on an AVIC D3 with a Bose system limits the volume output.
It has been suggested that you use speaker level out instead. Does this cause any distortion? Would it be wise to also use the Scosche SLC4 adapter along with the speaker level outs?
What kind of car?
There are several versions of the Bose system that have different amplifiers. For example, recent GM trucks and SUVs have either the LUX or non-LUX Bose system. The non-LUX has just your basic "dumb" amplifier but the LUX system uses a digital amp that receives only constant-level signal from the head unit and all the volume, balance, fader, and tone information through the serial data line (the amp does all the signal processing rather than the head unit). Then there's the old Bose system used in early 90s Camaros - it had individual amps attached to each of the speakers.
What kind of car?
This is for 97 Maxima, which uses the old style of having individuals amps on each speaker.
Your best bet is to use the adapter you linked to in the first post. Not only does it give you the proper input level for the amps but it also handles the unusual common ground setup used by the older Bose systems (the D3, like almost all aftermarket systems, uses floating ground).