Thank you all for your feedback! I think the Sansamp PSA 1.1 is somehow "difficult" to dial in and to set up to sound great. When recorded direct, it offers a lot more bottom end but also high end in the form of fizz and it requires a substantial portion of EQing. I realized to get rid of the extrem low and high end by using it as a classical preamp, going into the Mesa 2:Fifty as a poweramp (or any other tube power amp?!) and tracking it with a descent cab + mic or with the Two Notes stuff.
Anyone of you has more suggestions or experineces on how to use the PSA 1 or PSA 1.1 in another way? Some people suggest a solid state poweramp and a FRFR system; other like it with a tube power amp; and some people use it for direct recording and blend these D.I. tracks with those tracks they recorded with real amps plus cab and mic.
As far as I know, Rammstein (Richard Kruspe) and Nightwish (Emppu Vuorinen) used the Sansamp PSA 1 with a Mesa 2:Fifty as a poweramp. So, maybe thats how the pros use it?!