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
yes, you have been vey helpful in me narrowing my down my options here so i can get started on this. i think i'll get a Fubar 2 as i dont have a need for the headphone, and then maybe i will try out that PSU a little later on.

Thanks for the tips!
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.