Your SP6 is not a very good preamp. My advice is to get a good more current preamp, something from at least the mid ninties as preamp quality took a giant leap at that time. As a general rule using a preamp is better than eliminating it even though this seems counterintuitive. If using a cheap preamp, eliminating one could produce better sound in some aspects but a good preamp will almost always be the route to better sound rather than eliminating one or for that matter using a passive one.
Should I eliminate my preamp?
I have been using my Audio Research tube preamp and Bryston amp to drive Magnepan speakers for years. Recently I added a Oppo blue ray player to my system and connected directly to my amp using the balance cables. The reason was to eliminate the signal having to go through another piece of equipment before it hits the amp. Am I wrong or what am I missing?