I know what I'd lose by going from my Yamaha receiver to the 990 (auto eq/user settable graphic eq), but what's there to gain other than a few more a/v inputs?

Well, you'll also lose the 1400's amplification, unless you're already using the 1400 as a pre/pro with separate amplification.

What will you gain? Pro Logic IIx, 7.1 analog input instead of 5.1, digital bass management on the 7.1 analog input, more flexible bass management, and of course the expanded video switching that you've already mentioned (an extra component input as well as 2 input DVI switching). I'm not sure how the AV sync works on the 1400 (if it is global or assigned to each input), but the 990's is specific to each individual input. I liked the Yamaha receiver that I had a few years ago, but I would expect the 990 would offer one difficult-to-quantify improvement: sound. The 990 is a really nice sounding piece of equipment, much like the P-965 (which has garnered widespread praise since its release) that the 990 is based on. Whether that improvement is enough to sway you to spend the cash for the upgrade is something of a personal choice, but there is a 30-day return policy - if you are on the fence and are OK with parting with the shipping cost, you can give it a try and return it within 30 days if the improvements aren't enough to win you over.

Plus you have Outlaw's support staff to help out, and of course the folks around here to bounce questions off of as well...

I have DPLIIx now.

The eq works superbly (both auto & graphic).

The 1400 sync is global, but I don't need it for any of my current sources.

Does the 990 have other setting for each input (such as levels, x-over, etc.)?

I have no problem buying 'net based companies product, BTW. I own a SVS PB12 Ultra/2.

The manual is online through outlaw's website.

I would suggest thumbing through that. I own a HTR-5790 (similar to your Yamaha). The 990 probably won't give you any more options you'll actually use BUT, I believe it would sound better.

Even without the eq? The Yamaha's eq is a night & day difference in sound quality after setting it up.

An EQ can helpful in dealing with room problems, but it isn't a magic cure-all - and no matter what else is happening, you will always be relying on the signal that is originally produced by the DSP, DAC's, and overall signal path (not to mention the amps).

The Yamaha that I had a number of years ago isn't a fair comparison to the 1400 you have now - it was a Pro Logic unit from around 1997. However, the move from a good Dolby Digital receiver to good separates will typically yield an improvement in sound. That's likely to be even more true if the receiver being replaced was powering the speakers. (Are you using the 1400 as a pre/pro only right now, or are the 1400's amps driving the speakers directly?) I've had my 990 for over a month now (seems like longer, but it's been a crazy month or two), and I am still extremely impressed with how it sounds.

The 990's channel trim and crossover settings are global, plus there is a global two-channel sub trim to reduce the sub's presence with stereo modes. AV sync is typically caused by video processing, so if your processing takes place downstream of the video monitor output from the receiver a global sync is fine - but if the problem is video processing in a source component such as a DVD player, line-doubler, or HD receiver, then you really need the AV sync to be independent for each source. Most folks don't need it, but if you run across a source that does need it you'll be real glad you have it.

My 1400 is just used as a preamp. I have a Harman Kardon Signature 1.5 (200w x 2) for my Paradigm Monitor 11 v.4's, & a Harman Kardon Signature 2.1 (100 x 5) for 4 Paradigm Monitor 5 v.3's & a Paradigm CC-370 v.3/Monitor 5 hybrid.

The 1400 lip sync is global, but I don't need it for any source. I only plan on changing 1 source...changing from the current PS2, to the PS3 once available.

The 1400's eq (both parametric in auto calibration & user settable graphic) has made a night & day difference in the sound quality >60 hz. I plan on getting another SVS PB12 Ultra/2 & a Velodyne SMS-1 eq (once it is available).

I'm not really convinced I need the 990 as much as I'd need a Gefen HDMI/Digital audio switcher.

Here's the thing: RESOLUTION!
These processors are techinally something else, but more importantly sound like music should. When we are dealing in the digital world, the implimatation of high end D/A converters is far more important than the type of bells and whistles (though I am hoping for more bells with a nice software update). If The D/A converter is linear and has high resolution, I have not much need for high freq eq (we know this adds numerous kinds of distortion), of course there are external processors like Behringer, DBX, DEQX that correct room/speakers. I have all 3, but only use the DEQX (as 3 way active crossover/eq)
BUT, what's to lose? They take it back up to 30 days, nobody said different...