Will adding a preamp dramatically change my sound?

I agree with the other posters that for the most part one cannot make a blanket statement that an active vs. passive vs. no preamp is always best. Unfotunately, like most all suggestions, there are just too many variables. One must try different approaches to determine what is best for each owner, considering the variables of different equipment, cables, room and musical preferences.

I have tried several CDP's direct to amps with various results. First was an Audio Aero Capitole direct to ML amp which was very good. I tried (at the same time) a Wadia direct and did not like this. At the time that I ran both of these units both via direct and via preamps (Cary and BAT), I like the AA best direct with the Levinson amps but not as much with my BAT VK 60 mono amps, where the AA improved going through the preamps (to the BAT amps). The Wadia improved with either amps going through preamps. But the wadia had digital volume control.

I now own a GNSC modded Resolution Audio Opus 21 which is capable of running direct as well, but I have not really given this unit much of an opportunity this way. I run it through a Calypso and it performs great. As an added bonus it has digital inputs.

If I were you, I would strongly recommend borrowing a decent to good preamp from a friend or dealer and trying the preamp route. In addition to giving you better overall performance, it may also help with your soundstage height issues and your Hawk speakers. The Wadia's sound stage improved significantly with a preamp in play. The AA was less noticeable in this regard (with the preamps I was running at the time).