There is no signal degradation between the 2 tuner or 4 tuner unit when I did extensive testing between the units.
On a side bar note, the newer model is actually a little superior over the previous generation in terms of sensitivity.
There were issues when this was initially launched, but with some firmware updates, it has been resolved.
However, there is a "bug" with the newer models - as when using both tuners all the time, one will drop off requiring the unit to be power cycled approximately every 2 days. This will resolve the problem, but it will occur again.
I am awaiting for the next generation to be launched.
The first thing is the 4 tuner unit is at a 3 dB disadvantage because it contains a 4-way split vs. a 2-way split in the 2 tuner unit. SD may have made up for that loss in the design of the quatro. Perhaps someone from SD will chime in with receiver sensitivity specs for 4 tuner and 2 tuner units.