DAC for a computer musician

Hello!

This is a newbie question but still a very important one.
I am looking for a audio-interface/DAC/ADC multichannel patchbay
for myself and ran into some problems trying to understand that what exactly was i looking for.
If i want to get sound out of my computer, i use a DAC which converts the digital signal into a analog one. What if i happen to have multiple, separate signals that need to be output for external processing, (then maybe fed back into the digital world and so on..)
So, multiple digital signals which need to be kept separate.
Do i need multiple DACs? or is one DAC capable of decoding multiple signals, separate, into separate channels?
I'm not sure but i think i understand the analog world a bit better: (correct me if i am wrong)
Having multiple analog signals which need to be converted into a digital signals, i need an ADC which supports multiple channels (multiple ADCs, one per channel?)
If i need to have the analog signal amplified before fed into the system (the original signal is weak and should be amplified in order to keep it clean from noise) i am in need of a preamp.
As a computer musician, the preamps are not the most important thing except if you're working with field recordings, sampling and so on, which needs a lot of analog-to-digital converting and use of microphones.
Of course, if you use external processing where you use a digital signal, then output it for analog processing outside the digital realm and then feed it back, you need to make sure the analog signal is clean or amplified before feeding it back into the digital realm trough an ADC in order to avoid noise.

I'm confused. Do i need multiple DACs in order to get multiple separate digital signals outed as analog ones on different channels?
Most DAC's have only one or two channels plus a headphone channel.
What if i have multiple DACs? Can i use them all simultaneously to decode the signals or is the system only capable of using one at a time? (with it's channels, if it happens to have many?)
What is a good DAC/ADC patchbay/audio-interface/headphone-amplifier, with many channels and stable drivers? No need for preamps?
Or do i need to get many? Does the drivers conflict each other then if i use some systems from different manufacturers that are not designed to be daisy-chained or used at the same time on the same system?

Which digital signal output system is the best for such work?
There is many, of which i understand none. USB, SPDIF etc etc..