There isn't really a single source of information that covers all of these, in part because in some cases (HDMI being a prominent one) the technology is still in flux.

First, iLink is also called FireWire or IEEE-1394. The interface itself is used for a wide variety of things - DV camcorders, computer peripherals, and so forth. It was accepted as a means of making a digital connection between player and receiver for DVD-Audio a few years ago, although it took another year or so to hammer out the required encryption. Once that was all done, 1394 could be used to replace the half-dozen analog audio cables used by most DVD-Audio player owners. SACD took a little longer to come on board with 1394, but they do now also allow 1394 to carry digital SACD signals. There are a few players around that support a 1394 output for DVD-Audio and SACD (most don't, but you can find some that do). The 990, however, is like pretty much all of the surround processors on the market in that it does not support 1394. When the Model 950's features were announced over three years ago, some people thought it was a disasterous mistake to omit 1394 from the design because it was going to be the next big thing and a processor without it would be a dinosaur. Today, 1394 remains on the fringes, with little or no presence on even the latest processors. Also, it's worth noting that there are a few processors out there that offer 1394 inputs but that currently do not support actually using those inputs for anything. This all sounds really harsh, so I should balance it out a bit - there are companies supporting 1394 for DVD-Audio and SACD. For example, Pioneer has used it on some products, including some of their flagship receivers I believe (their site is down for service, so I can't check the model numbers), and Yamaha offers 1394 inputs on the RX-Z9. Denon, on the other hand, developed their own proprietary link for DVD-A and SACD, which requires you to use both a Denon player and a Denon receiver - the latest versions of DENON Link support both SACD and DVD-Audio.

My post last night about HDMI audio was intended to reiterate one fact: HDMI can carry audio and video, but the standard for that audio is not resolved yet and therefore can't be designed for. HDMI video is carried on separate conductors from the audio, and when you connect an HDMI cable to a DVI adapter, the video passes through while the audio is abandoned. In this scenario, you would be using a separate audio connection of some sort - today, it would be a coaxial or optical digital audio cable.

Nobody likes obsolescence, but you have to look at how you will use the product. Will you be putting it in a rack with a universal DVD player equipped with a 1394 digital output? If so, you may want to look at some of the (more expensive) flagship receivers that offer 1394. There may also be a few mid-level receivers with 1394 that could be reasonable alternatives, but then you have to decide if you are trading sound quality for a single feature. Are you really, truly interested in your next processor having HDMI inputs that are compatible with high definition optical discs (whatever format they may appear in)? If so, are you willing to wait for the year (or years) it will take for that standard (and the associated optical disc format) to be settled and products to be released with it? One danger that has always existed in the consumer electronics world is the wait for the next big feature. You can keep waiting forever, because as soon as the feature you wanted arrives there will be another one on the horizon. Or you can find a product that suits your needs well now, and spend the intervening months or years enjoying that product. For some people, their current gear is such that they can happily wait. For others, their preferences steer them toward other products (like the Yamaha RX-Z9, perhaps, or an all Denon system with DENON Link). You have to evaluate your personal needs, however, and not assume that one person's strenuous objections (or one person's shining praise, or even one person's utter indifference) must also be yours.