this may not be the most conclusive response, but i am in the same boat as you. i recently purchased a cairn for cdp that allows you to run amps directly. i also purchased cairn's nanda preamp and mea monoblocks as well. the fog is currently powering the meas directly and i am absolutely loving the sound! (possibly more than with the preamp in the middle, and it is a fine preamp for the price). like budrew comments, there are differences, and very noticible ones at that, it really depends on your personal preference and system synergy to determine if you 'need' a preamp or not. i have not conclusively ruled the preamp 'out' of my system, but may be on the verge of doing so, and possibly never looking back? (i aspire to the likes of kenscollick's wadia based system above ;) ) but i can only suggest that you listen to your system both with a pre in and out, i believe you will find the experience interesting if nothing else...
To preamp or not to preamp?
I am pulling together a two channel system that will also have a home theater function. At this point, I am only going to have one source- a CD/DVD player. I have noticed a few source units (such as the EAD DVDMaster 8000) that are able to connect directly to the amp and eliminate the need for a preamp. I am trying to understand the pros/cons of such a configuration. Does anyone out there have experience running a system without the preamp that they would like to share? System is under construction and so far includes Quad 989s as mains with dynamic Quads to cover the other three channels and a Levinson 334. I am looking to spend less than $4000 for the source unit.