A/D converters

[wahfreak]

I need a little schooling on A/D conversion...nothing technical.

Bottom line is I'm looking for something better.

I have a relatively simple set up in my basement for recording. I'm using 2 channels of SCA pres > line ins of my Presonus Firebox for conversion > DAW via Firewire.

I use Sonar 8 in a semi treated 12 x 16 space (bass traps and absorbers and monitor through Adam A7's. I use Peluso R14 and AT-4047, SM 57 mics for various tracking purposes.

My thought is to ditch the Firebox but I would need some sort of conversion. Lets just say I buy an RME ADI-2. It has SPDIF out but I don't have a SPDIF in on my DAW so do I need another sound card/interface with SPIDF in? If so, does the multiple conversion cause a problem?