I haven't had a chance to really give it a try yet to see how it compares to the 6.1 formats like Dolby EX, DTS ES, the 950's Cirrus Extra Surround (CES), or even DTS NEO:6, but I am curious. I'd also be curious to hear from a Lexicon owner (or anyone with a higher-end HK unit) who has been able to compare it to Lexicon's Logic7. Several people in this forum who have used it have clearly preferred it over Dolby EX, DTS ES, and CES. Maybe I'll get a chance to try out a Model 990 soon and form my own opinion.

Just to make sure we are all on the same page, Pro Logic IIx is a cousin of Pro Logic II. Where PLII allows you to generate true 5.1 channel surround from a stereo source, Pro Logic IIx takes 5.1 channel sources and creates stereo surround back channels. Pro Logic IIx can be applied to any 5.1 source - including Dolby 5.1 and DTS 5.1 sources. Model 950 users might directly equate Pro Logic IIx to an advanced version of the 950's CES, both in how it functions (taking CES's mono surround back signal and turn it into left and right stereo signals) and when it can be used (both can be applied to any 5.1 source passing through the digital domain - obviously, they can't be used with a multichannel analog input).

Would I upgrade just to get Pro Logic IIx? Personally, I wouldn't, but it might be a contributing factor in an upgrade if there were other compelling reasons to do so.