The OEM amp is not bridgeable so I don't think you should try to do that. You risk damaging the OEM amp. Now the signal to the underseat woofers is stereo, at least in the midbass frequencies and I'm sure it is mono in the bass and sub bass frequencies. So... If you are running and add-on sub in the trunk in conjunction with the OEM woofers, then it think it would be ok to tap only one side of the amp outputs, BUT if you are externally amping the underseats then you would lose some stereo separation in the midbass range.
For those who are having issues with the LC2i, are you adding bass boost from the head unit EQ??? If yes, that may be your problem. If not, the LOC may not be capable of handling the output of the OEM amp.
Mobridge DA2 > JBL MS-8 > ARC XDi 600/4 > JBL Gti 408 Mids & Vifa XT19 Tweeters; PG Ti2 1600.5 > Morel HCW-10 & IDMax 15