Here is some info that might be helpful:
1) It seems that most subs do not connect their L- and R- speaker level inputs together. If you have a DMM, you can measure
OHMS between these two jacks and confirm. Ideally, there should be at least 100 ohms between them. It's usually higher than
2) If you measure that the sub does tie the L- and R- speaker inputs together, you can still use them if you put a resistor in
series between the L- cable and L- sub's input jack, and the same value resistor in series between the R- cable and the R- sub's
input jack. I'd try 100 ohm (1/4W is fine) resistors, so the resistance between the negative speaker inputs is 200 ohms. This
is plenty and should work well, and the speaker level input impedance on subs is still quite high.
3) If you are running two separate subs, then you can connect the LEFT channel speaker outputs to LEFT sub, and the
RIGHT channel speaker outputs to the RIGHT sub. The negative speaker posts of the subs would not be connected in this
case (as long as they are not internally connected to the power cables earth GND prong - which would be very unlikely),
as you are connecting to two different subs.
4a) If you are using the REL sub with the 3-wire speaker level inputs, I believe the best way to do it is to connect
the L+ to L+, R+ to R+, and the GND to the RCA GND of LIO (e.g. use an RCA plug with the REL GND wire connected
to only the GND of the RCA, and do not connect the signal (hot) of this plug to anything). Then just plug it onto one
of the unused RCA jacks on the back of the LIO.
4b) Others with REL subs have reported that they connected the GND wire of the speaker level cable of the sub to either
the L- or R-, and it works fine that way as well.
I believe that such an important issue as subwoofer high-level input incompatibility should be clearly stated in the description of the amp module, as well as in the manual.
It is certainly mentioned in the LIO's owner's manual already. I will check the website and add it if it is missing. Thank you.
I hope this helps,