[scharfis_brain]

I cannot tell for sure (tendency goes to clip A) which is the 180 or 90 degree clip because I curently have no possibility to play back the AC3 in direct 5.1 off my PC.

but anyways this is NOT a fair comparision.

fair would have been:

Each downmixed with:
Lt = FL{0°} + 0.7071 C{0°} + 0.7071 LFE{0°} + 0.866 SL{180°} + 0.5 SR{180°}
Rt = FR{0°} + 0.7071 C{0°} + 0.7071 LFE{0°} + 0.5 SL{0°} + 0.866 SR{0°}
and
Lt = FL{0°} + 0.7071 C{0°} + 0.7071 LFE{0°} + 0.866 SL{+90°} + 0.5 SR{+90°}
Rt = FR{0°} + 0.7071 C{0°} + 0.7071 LFE{0°} + 0.5 SL{-90°} + 0.866 SR{-90°}

or Rockarias style:

Lt = FL{0°} + 0.7071 C{0°} + 0.7071 LFE{0°} + 0.866 SL{0°} + 0.5 SR{180°}
Rt = FR{0°} + 0.7071 C{0°} + 0.7071 LFE{0°} + 0.5 SL{180°} + 0.866 SR{0°}
and
Lt = FL{0°} + 0.7071 C{0°} + 0.7071 LFE{0°} + 0.866 SL{+90°} + 0.5 SR{-90°}
Rt = FR{0°} + 0.7071 C{0°} + 0.7071 LFE{0°} + 0.5 SL{-90°} + 0.866 SR{+90°}

but you are testing two types of four concurring types.
the traditional mixing with 180°
and rockarias inverse mixing with 90°

And I think this is perfectly audible when you can hear "weapons loaded" at the very beginning of the sample.

sample A lets it sound from the center.
sample B lets it sound from the surround.

But this is not due to the different phases but more due to the reason that one of the surround channels (in relation to each other) become inverted with your 90° matrix. (IMO)

(this is the thing I always tried to explain as center surround issue to Rockaria. But it seems to be a slightly different effect here)

so would you redo the samples, please?