Using Aux vs CD input on Audible Illusions preamp

I own an Audible Illusions preamp. Read somewhere that it was preferable to plug the CD player into the preamp's Aux input instead of the CD input. I've experimented with both and only notice a difference in gain. Is the Aux input recommended; and, if so, what should I expect to hear?
The CD input uses a resistor in each channel to cut "Digital brightness" from low cost CD players according to the manual supplied with the Audible. I found it to roll the highs just a touch. The Aux input is purer in as much as there are no resistors. I personally like the tape input. It represents the straightest path.
As far as which one to use, it is up to you. If you don't hear a difference, then pick one and go with it. All of the inputs end up at the same point in the circuitry.
I'm somewhat surprise you don't hear the slight roll off when comparing the CD and Aux inputs, however.
Thanks for the explanation. I'll try the tape input. My speakers (Essence Super Gems) have great midrange but are a tad shy in the high frequencies. So my system needs all the help it can get in the high frequency area. Only downside is that the volume pots are now at 7 (on a clock face) and I have to almost stand on my head to adjust the volume for CD play (versus between 8 and 9 when using the CD input). Love this preamp but sure wish it had remote volume control!
Audible did add a remote volume to their new L-2 preamp. The price also jumped up to $2495! I was hoping at some point that an upgrade for the 3A would add this also. I noticed its price has gone to $2795. You're right, it would be nice. I do love the sound of this preamp but I have been tempted to find one with a remote.