Found this awhile ago on AVSForum. Tangentially related to the Class D AMp discussion.
http://www.avsforum.com/avs-vb/showthread.php?p=16599598&posted=1#post16599598Warning to REL owners with Class "D" amps and/or receivers of damage due to improper ground.
The following situation can cause damage to your audio equipment. If you use regular "High Level" cables connected to any of the main outputs on a Class "D" amp or receiver, there is risk of damage due to improper grounding. However there is no risk of damage if your using the RCA type connection while hooked up to the low level connection.
If your using a newer REL sub bass system that's designed for both music (high level input) AND movie sound (.1 LFE Channel low level RCA type connection) while connected to both connections at the same time, AND your using a class "D" amp or receiver, you risk damage to your audio equipment with only the High Level Input connection.
Again, the issue being proper grounding. Hooking the black wire of the "High Level" cable to a phono ground will not help. Hooking up a RCA type connection to the black wire and attaching it to any of the unused RCA connections on the back of your amp/receiver will also not help.
The way to properly hook up your REL to a class "D" amp/receiver (while using the high level connection) is to use a "High Level Digital Cable" available through your local REL dealer. This is a "new" situation and the "High Level Digital Cables" are only being manufactured on a case by case basis. The word "Digital" is not to be confused with the type of signal being sent through it, it only describes the type of cable to be manufactured. Many local REL dealers may not be aware of this and will have to contact Sumiko for further information.