You need two rules, the first should handle email with a spamscore higher 10, but you already have this.?
The next rule looks just like this:
From: Anybody
To: Anybody
When: Always
What: Spam 6
Action: Quarantine
If you do not want to use the quarantine, you can also block these emails so that the user will not get them - and you can add a BCC, sending a copy to a special archive emailbox.
From: Anybody
To: Anybody
When: Always
What: Spam 6
Action: Block, BCC to myarchive email box