I run a Tascam 388 into a Echo Audiofire 12 into Protools. I have the 1173 and have been trying to get more pres but wanted to upgrade my A/D converter for more channels as a get more pres. I've been thinking about getting the Lynx Aurora 16 I/O D/A. Would love to hear some experiences with that I/O or some suggestions on some other 16 channel A/D converters.
I have both the Lynx Aurora 16 and the Apogee AD16x/DA16x pair. All are fine converters and solid performers. Although discontinued by their manufacturers service is still available. The Aurora 16 is a 16-channel AD and DA in one 1U chassis, while the Apogee units are separate 16-channel 1U chassis. So, basically the same capabilities and the same total pricing on ebay. The primary interface for both systems is AES/EBU digital audio. The Apogee units also have ADAT-S/MUX built-in. Plug-in expansion cards were made for other interfaces but, other than ProTools HD, they can be hard to find. Both systems are pretty easy to set-up and require little, if any, operator intervention.
(We are AES/EBU, using Lynx AES16e interface cards in our computer and lots of impressive 25-pin connectors and beefy cables which give us a serious, professional aura. Ha Ha)
If you only expect to have a few outboard hardware units, you might consider just adding another small interface with a TB, USB or Firewire connection. Also, a patch bay might be the best solution if you only plan to use a couple of pres and compressors at a time. Remember, you can connect a pre- directly to an EQ and then to a compressor before you need an interface into the DAW.
I don't have experience with a lot of different converters, but if you are on mac I highly recommend that you check out Metric Halo. It's rock solid, sounds amazing and their commitment to updating their hardware is unique.