That may be it. There's also seems to be a loose consensus that the Plus/Pro models have a built-in amp to avoid this, but it has been over-amplifying for some.
Originally Posted by RusRus
I've searched but found nothing. I think the loss of signal strength may be due to the signal being split over four tuners instead of just two.
*Coming in 2016: TiVo introduces OneTiVo with OneWay - There will no longer be any pesky choices to make. TiVo will determine what you watch, when, in what order, and content source.