I thought so too, however, It's not mapping A1-A2 (also tried with B1 and B2) correctly. I have tested this by pulling out the RCAs while playing music in discrete or stereo; when I pull out A1 I get no sound at all, if I pull out only A2, the sound is unchanged.

The strange thing is when DSP is set to Trifield, it is making use of A2 - however - A1 if coming out of the FL and FR, and A2 is coming out of the center channel.

Speaker Systems:
1. 2xDSP 8000s, DSP 5500C, 861v4, HD621
2. 2xDSP 6000s, HDMI Switch > Atlona HDMI De-embedder
Headphone Systems:
1. Audeze LCD 3, Stax 009, Chord 2Qute > Violectric 281 > Stax 717
2. Audeze LCD XC, Fostex TH900, Bel Canto Reflink > Chord Hugo > CI Audio Passive Pre, Auralic Taurus
Sources:
Oppo BDP 93 and 83, Project Carbon TT, J River