Why don't you contact the USA distributor?
www.bluebirdmusic.com
Maybe you can order the woofer from them. I would use the same 4 ohm one. Otherwise one channel may end up sounding louder than the other channel at any given volume level of the 6 ohm one is used.
www.bluebirdmusic.com
Maybe you can order the woofer from them. I would use the same 4 ohm one. Otherwise one channel may end up sounding louder than the other channel at any given volume level of the 6 ohm one is used.