Marty,
I don't know anything about tubes, but I will tell you that manufacturer's recommendations for speaker placement are baselines at best. They simply can't recommend best placement for the variety of rooms that their speakers will find themselves in.
Chances are that you have your speakers and/or listening chair in a bass null. Go to Radioshack and get an ANALOG (the one with a needle and old style analog dial) sound pressure meter and a test CD and take readings at different speaker and listening chair positions. If you have never done this, I GUARANTEE that you can improve your frequency linearity (and imaging) significantly and you will probably end up with both the speakers and your listening chair at very different positions than they are now.
There is no amount of equipment changes that can approach the positive benefit of finding the best placement positions for your speakers and listening chair in your room.
I don't know anything about tubes, but I will tell you that manufacturer's recommendations for speaker placement are baselines at best. They simply can't recommend best placement for the variety of rooms that their speakers will find themselves in.
Chances are that you have your speakers and/or listening chair in a bass null. Go to Radioshack and get an ANALOG (the one with a needle and old style analog dial) sound pressure meter and a test CD and take readings at different speaker and listening chair positions. If you have never done this, I GUARANTEE that you can improve your frequency linearity (and imaging) significantly and you will probably end up with both the speakers and your listening chair at very different positions than they are now.
There is no amount of equipment changes that can approach the positive benefit of finding the best placement positions for your speakers and listening chair in your room.