Before you make too many changes to fix your "problem", make sure your 703s are fully broken in. IMHO, B&Ws need some serious time to really break in, and until they do, they sound a bit conjested (and may accentuate a perceived brightness). If you've only been casually using your 703s since acquisition, I'd bet they are nowhere near broken in. It took me 3 years of casual use of a HTM-2 to tonally match a set of N805s.
Also, one of the most ignored component of systems (IMHO) is the room itself. Toe in is but one consideration. Check your speaker distances from room boundaries. What's on your walls / floors? What type (and how much) furniture is in your room? Unless you look at your room with a critical eye (and ear), you may be playing the hardware hokey-pokey to no avail and no matter how much you "upgrade" you may never be happy (unless you find that magic combination that compensates for your room).
If I was going to begin to swap hardware, I'd recommend re-evaluating the cables you're using (and silver cable is probably not the way to go). I really like the older PS Audio X-stream interconnects (and have them cryo'ed if possible). I don't find they roll off the highs, but they have a full, robust sound that compliments B&Ws articulate nature. I've built my own speaker cables, so I don't have any recommendations there.
Finally, tube rolling may be a (much) cheaper alternative than speaker / amp / cable rolling. Rolling the 12BZ7s in the Sixpacs or the 6SN7s in the AE-3 DJH may be the way to go.
