Hiya BIG_GEOFF,
I guess my reply is a little late coming, with all sorts of things happening around here my pc time is limited. Interested to hear the various comments re: painting the imperial. I too rollered mine, seeing as I used particle board for the panelling. Jake and I painted many of the interior panels before assembly, leaving only narrow, bare strips where the panels and the braces would be glued and screwed. After filling all the screw heads and seams, our choice of colour was black undercoat, followed by a rich black hammer finish gloss. I think it looks superb. Definately roller is the way to go. I only wish I thinned the hammer paint slightly, it had a tendency to pull some fluff off the roller brush here and there.
I've done a few speaker grills in the past, it's not too difficult. I bought the cloth through the various electronic hardware suppliers here in Oz, it is is invariably black. I had a browse through various manchester stores in town and never saw quite the same cloth, some might do the job, but perhaps not look quite right. Of course, you don't have to use black!
I use 1/4 round wood, about 3/4 radius. Glue and screw the corners. Extra bracing across the middle of the frame is optional, you don't tension the cloth so much that it is going to bend the frame. Paint the frame flat black (If you are using black cloth).
I also use the little clip on 'noddies' near the corners for frame removal. They only cost a couple of $$ and are easy to install. Fix the 'male' end to your frames - suitable hole and some glue, then lay the frame on the speaker box and mark where the 'female' insert will be located. etc.
Oh, we didn't cover the Imperials, they look just fine as they are. Standing with the speakers on top keeps all the good things out of reach of little hands. (Oh, and dogs >:(

).
If you get stuck with the grill cloth, give me a yell, I may have some laying around.
Cheers,
Gazman.