Ok, I almost like this:

subs(2*<g.P, g.Q> = pq.<alpha, beta)>)

although using subs is this way to avoid evaluation is not much less obscure than what I wrote at first. I do have one problem though. How do I avoid having '2*<g.P,g.Q>' evaluated as '<2*g.P,2*g.Q>' without emitting a bunch of unevaluated typesetting code?

The typesetting example looked particularly horrendous to me!

I really am trying to like Maple document mode - honest. :-(

No. I mean typesetting a matrix expression. I mean something literally like this, for example:

  | 1  2  3 |   | x1 |   | b1 |
  | 4  5  6 | . | x2 | = | b2 |
  | 7  8  9 |   | x2 |   | b3 |

But prettier, of course!