No subwoofer output from Yamaha receiver

[Nexus7]

I'm unable to coax the following setup to work.
Receiver: Yamaha RX-V630
Subwoofer: Mirage FRx-8
Source: CMI8738 on-board sound card putting out PCM and 5.1
Connections: Sound card optical out to DVD in of receiver
"Subwoofer Output" RCA on receiver to line level in of sub (also
tried crossover RCA in on sub)

The subwoofer is silent. I have the mains set to "small" (also tried
"large"), and subwoofer/LFE set to "both" (also tried "swf"). With PCM
input, the receiver display lights up L & R icons, whreas with 5.1, it
lights up L, R, C, RL, RS & LFE. The speaker levels are at defaults
(mains at "normal", sub at 0 - this can go from 0 to -20 dB).

If the mains are set to "large" and the mains wires are connected to
the speaker-level input on the sub, it works (the cutoff and sound
level knobs also work). The RCA patch cable is also good, because I can
use it to connect the receiver to the sound card using the coax digital
input and it works the same as optical.

I've read that some Yamaha receivers have bass management problems, but
I don't know if anyone's had problems with this particular model. Any
ideas? Thanks!

[Nexus7]

I. Care wrote:

> Is this a powered sub? The Sub output appears to be a pre-out and needs
> to feed a sub amplifier, not drive the sub speaker directly.

Yes, it is a powered sub. In addition to the speaker-level
spring-loaded inputs (1 pair each for R & L), it has an RCA in marked
"xover" and another RCA in for line-level input from the receiver.

I hope I don't have to connect the receiver to a pre-amp, and the
pre-amp to the sub?