Seeking advice/tips on improving sound quality

I guess based on everyone's feedback the lowest common denominator is a DAC. For some odd reason my Arcam RDac doesn't jive with the Macintosh pre amp and when I turn up the volume all the way to the max I get a sound level that is moderately acceptable. Hence I am a little reluctant to purchase a DAC only to find that I am still experiencing the same issues. I will take my C27 to local dealers to find a day that can actually work well with it.

Do you have the system on a dedicated line, and if not, have you ever considered doing a dedicated line with upgraded outlet?

The weak link is your source.  There are various options as mentioned CDP, DAC, build your own server which will sound better than the MAC, etc.  Best option is a really good DAC IMO this will give you the biggest improvement.  You really don't describe what you are searching for so it is hard to know what to advise you on.  It is best to mention what music you listen to and where is lacks what you would like to change.

Happy Listening. 

Bigkidz, you hit it on the nail. Unfortunately I don't know what I am looking for myself outside of just exploring what can help improve the current sound. I predominantly listen to classic rock and roll (mostly Floyd, Led Zep, Who) and then jazz (Dave Brubeck, Miles, Monk etc) and then a few odd categories in between at times. My desire to improve the sound came up when I noticed differences between CDs that I was playing to the corresponding recording streamed from the iMac. The difference was primarily in the separation of instruments which sounded very good irrespective of the source on the jazz recordings but not so much on the rock and roll ones. Hence I started questioning whether the recordings themselves were the culprit or it was something in the setup that needed a boost...Looks like all roads are currently leading to a good DAC so I will explore that option. I guess my final goal is to have the ability to get CD like sound but through the convenience of a music organizer like iTunes etc. so that I can listen to various different songs/artists without loading/unloading cds. 

Are you using a macintosh CD player?  It sounds like you definitely have a source problem. If a CD player sounds good through your pre-amp, I don't think it's your pre-amp or anything down stream. Let us know what kind of budget your thinking about and I'm sure people can recommend some good DACs in that range.