Sun Audio SV-2A3:: Direct or not?


How many Sun Audio SV-2A3 amp owners use a preamp in their system. Is there a sonic advantage in connecting a CD player or other digital set-ups directly to the amp bypassing a preamp? When used with a preamp, should the gain on the amp be turned all the way up?
Thanks for any info.
pogi
I use a custom built tube preamp with the Sun SV 2A3, which I also mod to replace 6SN7s with WE 417A tubes. They sound perfectly awesome with spatial, detailed and sweet.
Average price of a pair WE 417A right now on ebay is USD$60-80. Whereas top line of 6SN7s are sold with untoucheable price USD$150-200 like Mullard ECC33 or rare TungSol VT231 round plated. To me WE417A is best choice of input tubes for 2A3 and/or 300B amplifiers. Do not underestimate the little tube like WE417A/5842!!! You will be surprised if you know how to mod.