Tube recommendation for Audio Research LS-2b?

I have an LS2B-MKII and have compared the stock Sovtek 6922 with an Amperex 7803 (PQ/Orange). The Amperex was much more detailed but added a slight sibilance. I'm not sure if the tube was the issue or whether the preamp needed a bias adjustment. (the seller said the tube was NOS and tested well).

Yes a large '253' is etched vertically near the top. The orange labeling is easily scratched off, however.