Computer output to DAC, which route?

Use a firewire device. Firewire is the best connection protocol on the planet and their are lots of great DAC options available.

Weiss firewire DACs

Echo Audio firewire DACs

just to name a few. Excellent performance for the price from the ECHO firewire interfaces.

http://www.home-speaker.net/diyhometheaterspeaker.html

Grace Design m902b headphone amp and ASUS Xonar HDAV 1.3 soundcard. The HDAV 1.3 (several minor variants) is the only line licensed to decode and transmit the audio from Blu-ray at full resolution. You will need Arcsoft TotalMedia player to do this. The soundcard has an S/PDIF out and the amp has an S/PDIF (and an AES) input. The headphone amp also has USB input but USB is limited to 16 bit/48 kHz, which is just not good enough IMO. The 'b' in the headphone amp's model number is for balanced outputs to use with active speakers.

The one box solution:

I have been a pretty hardcore analog devotee, but loved the convenience of digital. Cut to the chase: If you have a Mac server with firewire, buy yourself a Metric Halo LIO-8. There is a learning curve associated with pro gear, but in this case it is worth it. IMHO playback at 44K is easily competitive with an Ayre QB-9, and you can do so much more. It has 8 channels of analog and digital IO, runs at 24/192 and will let you record whatever you want completely transparently (at least to my aging ears). Use Pure Vinyl with it to archive and play records better than direct feed from my (RHEA) phono pre. Sell your current (QB-9) DAC and use it to play back all your digital files. Grab some batteries and do some location recording (haven't done that, but am thinking about it). It is not cheap, but a totally amazing box that is a very good value and unlikely to be outclassed for quite some time. Just don't expect a fancy box to put on display.

I have a question. I have a REGA DAC and a Macbook. I would need either a USB-SPDIF converter or a good mini-toslink to toslink cable. Any suggestions for something not too terribly expensive?

I'm in a similar situation... I have a new Macbook Pro and the DAC from my Audio Aero Capitol with SPDIF inputs. I'm leaning towards getting the Halide Design USB-SPDIF Bridge ($450) along with Pure Music software that works with I-Tunes($129). I have not pulled the trigger yet, but like the idea of the Halide Bridge because it's a USB/SPDIF convertor and a digital cable all-in-one... so no extra digital cable is required, unlike most other SPDIF convertors.

Would appreciate input from users of the Halide Bridge.