I think both are reasonable choices, and the best way to decide is to compare the two a few times and see if you have a personal preference. Why do I suggest this in spite of the fact that using NEO:6 would keep us solely in a DTS-licensed decoding environment? There are two things that cause me to leave the door open. First, both are being applied after the DTS decoding, so they are acting solely upon the left and right surround channels to generate the surround back information, so mixing DTS and Dolby by using PLIIx isn't quite as unappealing at it might initially seem. Second, PLIIx has an advantage over NEO:6 when it comes to generating a surround back signal, and that is that PLIIx generates discrete left and right surround back channels rather than the mono surround back produced by NEO:6 (and by Dolby EX, and many other similar matrix processing systems).