Here's a low cost amp to feed more cans on the set, I use this...

http://www.boostaroo.com/store_detail.php4?id=14

Runs very well from the A1 to 3 sets of cans with piles of clean level for all. It has a 14" output cable.

There's a newer version to 2 sets, anyone have this one?

http://www.boostaroo.com/store_detail.php4?id=13

Cheers.

...and here they are on clearance at reduced prices ($17.99 and $29.99)

http://www.boostaroo.com/store_category.php4?id=5