Effects on the warranty of any internal modifications?

There is a way not to get double bass. Just use the 80 Hz analog crossover.

You can also use an ICBM for the entire unit. Config the 950 so that all speakers are large, with no sub (that reroutes the LFE to the mains). Then just connect the 5 but not the .1 of the 5.1 pre-amp outs of the 950 to the ICBM, and let it tell re-route the relevant info to the sub output.

Courtesy Dre J's solution for the Rotel 1066 on HTGuide and HTF...