CNMeow,
I've gone back to read up on the Plinius pre and amp you have. Two suggestions to explore based on my own experience:
1. You could look into Nordost Thor which was spectacular and not crazy expensive. i would NOT use your Pass SA103 with it! Just your CD, source. The amp is far too powerful and it will blow.
Specifically, the Nordost lowers the noise, grunge level; it also makes the individual musical lines within, say, an orchestral piece both more delineated...but also better integrated. In other words, rather than a blur of musical lines...you will start to hear individual musical lines that ALSO have a clear interplay with the other musical lines. Dynamics changes only in that noise floor is lower.
2. If you are looking for a wholesale step up in midrange clarity but retaining your Plinius apparent beauty, and also improve soundtage and dynamics...i would say consider preamp upgrade. Lyra Connoisseur, ARC Ref 5, CJ ET5 perhaps.
Why? I have not heard your Plinius myself...i just know that i have begun to understand why some say the preamp is the heart of the system. Moreimportant than i first realized. i noticed going from CJ PC14L to ACT2...but fully appreciated when hearing GAT. Stunning increase in midrange, treble, extension, dynamics. and with your amp...you'll be able to push what ever signal comes thru effortlessly thru to some amazing transducers.
my two cents.