The FAQ says the limit is 8 accounts per battle.net. So you ten boxers need to create 2 battle.net accounts and then merge them.

I am so happy they did this. I was going to post a suggestion for linking accounts so we can quickly mail between our multiboxed accounts and not suffer the 1 hour penalty. This may also mean we can mail account bound items between our boxed accounts also. So if you collect more stonekeeper shards on one account you can send the spoils to other accounts without having to pay $25 for a transfer.

Overall a big woot!