Connect Macs to analog amplifier?


I have 2 systems I need to maximize the sound quality from Itunes to stereo.
My main system is a Musical Fidelity A300 that connects to a G4 laptop. (Mission 735 speakers soon to be upgraded)

My secondary system is a Nakamichi receiver with Triangle Stella ES speakers
which connects to a new MacPro Tower.

Both the MF and the Nak have only RCA jacks and I need to find an affordable way to get the most out of my digital music. I was looking in the $100-$150
range and consider Blue Circle USB Thingee, Trends Audio UD-10.2, or M-Audio Audiophile USB. Im overwhelmed as there are so many ways to do this.
Suggestions much appreciated!
xistented
I had a Fubar II and the supplier power supply takes it to the next level. It's worthe the extra $110.
I have an iMac connected to an M-Audio Audiophile Firewire, Redwine Audio upgraded ClariT and some Triangle Zerius. This combination is the most enjoyable I have had regardless of price - I have a small room. I enjoy it as much as I do my vinyl - just in a different way.

I'm very happy with the sound from the M-Audio. I don't know if Firewire sounds better, but I think I will stick with that over any USB product due to the theoretical benefits.