I'm currently running a linux server into an Onkyo home theater system
using a USB-to-toslink device, and all is well. I'd like to migrate
to slightly different set-up. I'm planning to connect speakers in
four zones into a speaker hub with support for auto-muting volume
controls, and have wall-mounted volume controls in each of the four
zones. The linux server (a de-commissioned laptop) is in the
basement, and I'll need more power than the current Onkyo has, so I'm
thinking that I'd bypass the home theater system (saving that for
films) and go with an amp near the server. So, I'm wondering:

1. Can I connect the computer directly to the amp? For example, will
the computer work as a pre-amp, and I switch from the toslink approach
to a minipin-to-RCA jacks approach. Are there drawbacks to this?

2. If not, are there inexpensive pre-amps that will take the toslink
as input, and that I can then connect to the amp?

3. Are there better approaches than either of these that I'm
overlooking?

Thanks!

Yes, I have connected my old hifi amp to my pc to use the speakers
that the hifi came with. I plugged my amp into my soundcard 3.5mm jack
via a "3.5mm jack- 2xRCA" cable. This wokrs very well