line adapters are useless...since the inception of this post, I got one, did not work as stated, returned it. I sold the xover and gave up in the idea of running a passive pair of subs, with the xover and the extra amp. It is much easier to get a powered sub, with high level inputs, and run two pairs of cables from the speaker output binders of the integrated. Now, there is two sets of speaker cables, they run from the same output, one to a pair of low frequency limited sets of speakers and the other to the subs. Signals travel at the same rate, thus no timing issues. The sub that I got is very fast and powerful, so, I think I am getting everything I wanted and the motive behind me writing the post, without having to go crazy with multiple RCA wirings here and there. Now, the blended signal is most definetly seamless.
PAUL