I need help choosing a DAC

I'm new to the USB DAC world so I'm hoping you can help me determine which of your products is suitable.

Here's how I'm doing things now:

- Mac Mini
- iTunes for ripping and organization
- Front Row or PLEX for consumption
- CDs ripped at full AIFF or Apple Lossless or purchased FLAC
- Toslink cable from the Mini leads to an Integra Preamp (internal DAC) - amplification, etc.

When I want to the music to really shine, I use a BDP-83 as a transport and just listen to physical CDs. I love the Integra's DAC and just wish it had USB capabilities.

A/B comparisons between AIFF/Mini and CD playback reveal the following:
CD has better imaging and a wider soundstage, more detail and decay in the high end but still warm.

Do you think I will get better sound bypassing the Mini's sub par optical port and moving the data via USB? If so, which DAC is for me or is there a way to convert USB to coax (to Integra) without screwing the sound?

Anything that makes the music sound more digital or adds grit to the mids and highs is not desirable.