|Somehow I don't see upgrading just the antenna as helping to increase the range of a wireless network. It seems to me you'd also have to increase the signal strength too and the only way to do that would be to upgrade your radio(s) as well.|
If you've looked through all the settings and can't find a way to disable those two antenna's then you're going to have to contact the DD-WRT people and ask them. If they don't support their product, then perhaps there are some forums like this on the web dedicated to DD-WRT that you may find help in.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.