[LAU] problem with LFE output "leaking" into rear speaker

I have an interesting problem. I'm using optical outputs to a d/a with 8 output channels (Frontier Tango24), but I needed 10 output channels. So for the l/r rear channels I'm using the spdif outputs from my RME card connected to an Orei DA21 2 channel D/A unit. This seemed to work fine, but when testing I limited the Ecasound output to LFE only, and I noticed that somehow the LFE signal gets sent to the l/r rear amp in addition to the sub amp, and I hear LFE coming out of my small(er) rear speakers. (I put a 50hz high-pass filter on them for now, until I figure this out.) I'm guessing this might have to do with 32 bit vs. 24 bit output or something. Here's the line in Ecasound that outputs to Jack: -a:rear,LFE,sub_left,sub_right,center_sub,center_low,center_mid,side_low, side_high -f:f32_le,10,48000 -o:jack Any ideas? Thanks, John