Looking at simple set-up for iMac to preamp

Hello all - Without a total degrade of soundI am looking for the simpliest format to listen to internet radio through my main system. System is simple - CD to integrated or to preamp w/tube monos to speakers. All connections are standard RCA. I am certainly willing to spend the bucks if needed but if it is only a particular cable, adapter, splitter or the like I hate to re-invent the wheel. As above I want to connect the iMac into the preamp. Can someone spell this out slowly for me?
Assistance much apprectaied.
3.5 mm phone plug to stereo RCA cable. You can get this from Radio Shack (no affiliation whatsoever). Plug the 3.5 mm plug (like a mini headphone plug) into the back of the Imac, plug the RCA plugs into pre-amp or integrated, adjust gain at the iMac to approximate the same volume as cd, and voila'. You could probably pay for a fancy interconnect if you've got money to burn ;)
Does the iMac have a headphone jack? If so, and you said you wanted simple......

Most simple: get a mini to L/R rca plug (Radio Shack or?). Mini goes into the iMac headphone jack, the rca's go into an unused input jack of your preamp or integrated...Your done.

Next in line but better sound: The headphone jack on our Macbook Pro is both analog and optical. I would think it would be the same on the iMac. Use the headphone jack again but go optical out with a Toslink cable (mini adapter on one end) into a DAC and then into your pre.

Next and maybe the best: You didn't mention how far your iMac is from your pre. Near or far, Apple's Airport Express (around $100) could be the cleanest way. Check Apple's website for more info or maybe someone here can chime in.
I see Ths364 posted while I was typing mine. Ya got me :-)
The MAC optical outputs are great. You'd have to add a DAC, however.
IF the confuser is located away from the stereo, you could use an Apple TV or an Airport Express, either of which can be run in 'client' mode...that is, without a wireless network. I do that with my iMac and run the AE as a 'dead end'.
Minimum additional expense would be maybe 500$ for the AE and a DacMagic.
Get one of the HRT Streamer dacs. Simply hook the Imac via USB to dac and rcas from dac to pre.
I did the same just to listen to internet.
If your cd player has a digital in (optical), you can just run a toslink cable from the headphone out on your iMac to the cd optical in. This uses the dac in your cd player.

If not, you can get great sound running toslink to any outboard dac, then rca to your pre.

I also like Tan43's suggestion.
Try a Behringer UCA202 (usb out from the iMac, connect via analog RCA interconnects to the integrated). I'm using one in my office, and it's shockingly good for the money (less than 30 bucks).
Thanks all - initially I will go with the low down, dirty and cheap solution as layed out by ths364 and onemug. Nest I will try the Behringer by afranta. Other solutuins may come but with no Dac new equipment needs to be purchased. How about some of the Class D and T integrated's like Bel Canto with internal Dac's and what appears to be direct hook up to what I want to accomplish? I also read on the Cambridge NP3, looks interesting. It will nice listening to Jazz 24.org as I do at the office and just let it flow. I'll have it set up this weeked on the simple and go from there, thanks again.