Hey vthokie83,
Both the Backert Labs and AricAudio preamps are great pieces and Andy and Aric are first rate gentlemen. I have owned and reviewed preamps from both companies. The Backert Labs,using 12AU7 tubes, and AricAudio, using 6SN7 tubes offer a different presentation. The Backert Labs is lighting fast, quite detailed without being etchy, very transparent, and very pure in tonality. It reminds me very much of the Linear Tube Audio's David Berning sound. The Aric Audio offers those virtues, but because it uses 6SN7s its midrange is fuller and a bit more romantic. It really comes down to personal taste and system matching. I personally love the sound of1940's NOS 6SN7 TungSol black glass oval plates in my Motherlode preamplifier.
Because the S5.5 is so transparent you will hear the "flavor" you inject into the system using different preamplifiers or the tubes you select.
Teajay