How to decode 6-track APTX-100 (cinema DTS) with the correct channel levels

[little-endian]

[...]once the A->D conversion has taken place[...]

You mean "D->A" conversion, don't you?

[zoidberg]

Yes, well spotted

[Dr. Cooper]

Yep, use 32-bit floating point PCM instead in Foobar's export settings and attenuate the levels in an audio editor of your trust. This should avoid the clipping.

Just using "32-bit Float" in the Output Bit Depth-settings in the converter-settings should solve it? Right now it's just set to "Auto" and converts the files to 16 Bit WAV-files.

And just to point it out again, so there's no confusion: It wasn't the LFE that was clipping, it was one of the Surround-channels (IIRC Surround Left).