Pre-amp upgrade time?

Sounds like a used ARC Ref 3 preamp would seem to be a natural fit for your ARC amp, and the sound you are describing that you seek.

 
 I totally agree. An ARC Ref preamp would be an excellent match. I own both a Ref 110 and Ref 5se, just superb together. 

I think the SLP-03 was one of Cary's weaker offerings.  The SLP-05 is lightyears better.  I'd put it toe to toe with the ARC REF preamps.

I agree with Spencer. I just visited Backert Labs last week to get my EAR 868 repaired. I got a chance to hear Bob's Rhumba preamp while there. Very impressive. The "fastest" and punchiest tube preamp I've heard most likely due to his patented innovative power supply plus, I'm sure, his careful build quality.
I should add, I have no financial connection to his company. I went to his facility on the recommendation of a few good folks on this forum about 2 months ago. To those people, I say thank you again.
Best, Fred

Cary SLP 05.

My friend has the arc5se.

It was pretty much a tie, we compared it in the same system and the same time.

If you truly want something special as I have done and others 
check out a Direct Heated Triode preamplifier transformer coupled and fully regulated . Using a quality pair of 45 tubes, and 6ax4 rectifier tubes 
Lundahl transformer based withseperate power supply .  Every bit as good 
if not better to the Battery-capacitor Rosse Lio,which is almost $9500 now ? which BTW  can be ordered use several different tube types 
but the 45 is known for its depth and realism ,and noise floor well below
1%.  In the $6k range  This will compete without question the best of them. 
This is what a single ended preamp is all about .it will pick up detail like no other
i am working on having another one built  which can be built for $2k less  in one chassis ,and still unbeatable in its price class . Look up Radu Tarta .he  has been working with DHT ,and tube amps for  close to 40 years. Best of luck.