"My suggestion is that you consider trying your existing amps in a passive vertical biamp configuration...."If both of the "dual balanced outputs in parallel" are driven from the same output stage within the line stage, as seems very likely, the lack of bass weight in the vertical biamp configuration could very possibly be due to the impedance compatibility concern that I cited earlier. You may want to discuss that with Dan.
Al, thank you for your feedback. I have already tried this, while I gain bit of better separation in mid’s and high’s, the bottom falls out a bit. The low bass frequencies are not a weighty as they are when I run the amp in bridge mode.
Secondly, the LS36.5 is configured with dual balanced outputs in parallel to accommodate bi-amping or a sub with balanced inputs.
If he confirms that both of the output connectors provided for each channel are driven by the same output stage, and if he indicates that the output impedance of the line stage rises significantly at deep bass frequencies (as is very common with tube line stages and preamps), you may want to consider inserting some sort of a buffer stage between the line stage and the amps, that would provide high input impedance and low output impedance, and re-trying the vertical biamp configuration.
Regards,
-- Al