need help selecting the right preamp

Thanks for your input. I found a good solution after speaking with Apple tech support. The headphone jack line out from the imac actually doubles as a fiberoptic output. Toslink makes an optical cable with an adapter to make it fit into that headphone jack. I was able to hook up the other end directly into the optical input on the preamp. Good music :)

I have a pair of Polk LSI25 floor speakers, and a center channel LSI C. The room doubles as a TV/theatre room as well, hence the center speaker. Most of my music is mp3 format 320 bitrate, so I'm not sure if a high end DAC would add to the fidelity. I'm essentially using my pre/pro built in DAC with my current setup, since my connection is now fiberoptic from imac to pre/pro? Tube units maybe a little too fragile for my setting, because I have 3 little kids that like to sneak into the room, and a housekeeper that likes to bang the vacuum cleaner against the rack.