I have to say that I really question the validity of that statement. In fact, I'd go so far as to say that claiming "DTS (the company) does allow any receiver (or pre) to "matrix" a DTS 5.1 signal." is a fairly absurd statement. After all, DTS offers a matrix decoding scheme for DTS 5.1 sources: it used to be called DTS-ES Matrix, but more recently they've phased that name out in favor of applying NEO:6 to DTS 5.1 (both cases use the same matrix decoder).

I will say that Dolby does not require that Pro Logic IIx processors be able to overlay PLIIx onto DTS 5.1, but that many receivers and processors do offer that - it's an optional portion of the PLIIx spec, and is done downstream of the DTS decoding (at which point it isn't functionally any different than applying bass management, and saying that it violates compliance with DTS seems pretty hard to swallow). The same would be true of the Cirrus Extra Surround matrix decoding that your Model 950 can use in conjunction with DTS 5.1. I would most certainly not say that receivers and processors (including your Model 950, my Model 990, and countless processors and receivers from companies like Denon, Harman Kardon, Lexicon, Anthem, Arcam, Rotel, Yamaha, Sony, ...) are doing something wrong by offering the capability to apply matrix decoding to DTS 5.1 sources.