Thanks, all. Here's the response from REL to my question, FYI:
REL: "Thank you for contacting us. You can use an extension cord with your REL subwoofer, though it is important that the extension cord is rated to handle the current draws requires by the subwoofer. The extension cord should at least match the specifications of the stock power cord that is provided with the subwoofer, and these specs are listed below:
- 3 conductor (including earth ground)
- 18 AWG wire
- 300V voltage rating
- 105°C temperature rating."
REL: "Thank you for contacting us. You can use an extension cord with your REL subwoofer, though it is important that the extension cord is rated to handle the current draws requires by the subwoofer. The extension cord should at least match the specifications of the stock power cord that is provided with the subwoofer, and these specs are listed below:
- 3 conductor (including earth ground)
- 18 AWG wire
- 300V voltage rating
- 105°C temperature rating."