as far as just pre or no pre, I went thru a period where I experimented with and without preamps. I tried it without a preamp for a week, allowing me time to get used to the different sound. It could just very well be my ears are used to a certain sound which isn't actually that accurate as you would think adding a preamp is just adding more circuits for the signal to have to go thru etc, but for my earsI thought the preamp-less sound was 2 dimensional, it didn't have the layering, texturing etc that I was getting with a preamp.
Then I picked up a Conrad Johnson pv2ar preamp and it took my system to a whole new level and to be honest, I never thought I would own a system that sounded this good.
I have been to a persons house that had some really nice albeit vintage totl gear and he wasn't t using a preamp .Listening to it I was not really that impressed, was pretty much the same as my experience without a preamp, the music just sounded lifeless.
Don't see how a preamp does it (I am taking decent preamps of course) and I wouldn't consider my one small test indicative, but for me, besides the ability for more connections, I just really prefer the sound of a preamp.