Do I even need or want a preamp?

For over 5 years my home audio system had been stable. I used a Wadia 6 direct into a Jeff Rowland Model 1 with Synergistic Research balanced interconnects, out to a pair of Aerial 10Ts (Synergistic Research cables). I knew that the speakers could use more power than the Roland could give, and that the Wadia 6 was now pretty outdated. I recently replaced the Wadia and the Rowland with an Accuphase DP-57 CD player and a used Levinson 336 amp, plus replaced the interconnects with a pair of Tara Labs Air2. The end result was that the Aerials came alive and I am hearing MUCH more detail without harshness.

I brought home a BAT preamp to try out and have to say that whatever differences (other than volume capability) seemed quite subtle. The bass might have been a bit tighter, but it seemed like some of the ambient information was lost. Considering the $6500 list price of the preamp, I am trying to figure out if a preamp is even helpful for my system. The Accuphase has its own internal volume control. Never having owned a preamp before, I don't know what I was expecting, but improvement in the sound did not seem to be present with the preamp. I am now leaning towards not adding a preamp to the system, but want to know if I'm simply uninformed about any benefits that one might do for my current system.

Thanks in advance for helping me learn!