Err... audio digital I/O is NOT USB, FireWire or eSATA. Those are interface buses, and are used to connect things like an audio interface or an external hard disk to a computer. Audio digital I/O is ADAT, S/PDIF, AES/EBU or other proprietary protocol. From what I can de-cipher from your post, you should be looking at a computer equipped with an audio interface and running a program such as Cubase.

An audio interface such as the RME FireFace800 connects to a computer via FireWire and has MIDI, S/PDIF and ADAT digital I/O as well as 10 analog ins and 10 analog outs. You can use Cubase or almost any other DAW software for recording both tracks and automation.

Alternatively, it may be that you have in mind an all-in-one box that will record audio tracks and MIDI sequences, and can be connected to a computer.

Tell us a bit more what it is you are trying to do.

"Audio digital I/O is ADAT, S/PDIF, AES/EBU or other proprietary protocol."
I use an Edirol FA-66 currently, it would appear I need to upgrade to an audio interface that has a multitrack digital I/O. I am looking for a recorder that can sequence as well as multitrack (synced or not).

Also I would like to be able to use a plugin host as an effects rack, and be able to overdub, etc.

You can use your FA-66 for what you want initially. The spec says it has 6 concurrent inputs, but they have to be the right sort: 2 microphone/line inputs, 2 consumer-level line inputs on RCA connectors and one 2-channel S/PDIF digital input. In addition to these, you have MIDI I/O for your sequencing and automation. With no further hardware, you can record and replay 2 mic channels with MIDI sequencing.

Before laying out any further cash for hardware, I would do some more experimentation and get more experience with your current box using a program such as Reaper or Cubase. This will help you get an idea of what you actually need to achieve your goals.