That certainly explains some things... according to
this, your wireless card only supports 2.4GHz.
And to try to clear up your confusion between HEX and ASCII, I'll try with my limited (read: possibly wrong) understanding of WPA.
ASCII, aka passphrase, is a plain-text password that you specify for your network. This makes it easier to remember than the old WEP keys which were only HEX based. However, the password is never sent over the network and is instead coverted into a 64 character HEX using the password and SSID with an algorithm. I believe that HEX key is what's sent over the network. I don't think linux wpa_supplicant requires you to specify the HEX PSK, but allows you to do so. This is likely a security thing to prevent requiring your password to be stored in plain text on your computer (similar to how /etc/shadow just displays a hash for the system passwords instead of plain text passwords). If you're the only one using the computer or you don't care if others can find your WPA password, you're able to easily store it in plain text. If you want to hide that password, you're able to store it in HEX form, using wpa_passphrase to obscure it.
Again, I might be wrong on this, but it's how I understand it.
