I bought the DX7 package from 3D with my quad kit. When I unpacked it there were 3 receivers in the package and after puzzling over this for a while I just decided to use the biggest and baddest one (8 channel).
Question is what is the logic of three different receivers with one transmitter? The only difference seemed to be the number of channels available.
It really depends on the version of the receiver.
AR8000? , AR600 , AR6200???
Some Receivers have failsafe features, And some (AR500) have undesirable failsafe features, while some may have none.
The 8 channel RX is probably the one to go with, but this is just a guess since I don't know which specific RX units we are talking about.
Better details will yield a better answer.
Seems to be this package: http://www.spektrumrc.com/Products/Default.aspx?ProdId=SPM7800C
Which is to say that it came with an AR8000, AR6115e, AR400 MD2.
I used the 8000 but don't see much difference other than no. of channels and physical pages
The AR6115e is a 'park-flyer' short range RX...
The AR400, while it is a full range RX doesn't have enough channels for practical use with ArduCopter, but it also has an unfavourable failsafe behavior. The servo signal outputs on the non-throttle channel are removed! Yuk.
The AR500, & AR600 failsafe behave the same way as the AR400.
If one of these were to be used on channel 8 of APM, (ArduPlane setup for example), the hardware failsafe would be switched to manual because of the loss of the servo PWM signal, the hardware failsafe on APM would be forced into manual mode, bypassing any signals from APM.
The A8000 RX will provide a neutral position output (1500 mSec) during a failsafe condition...
Channel 8 is not used on ArduCopter because it needs the APM to be 'in the loop' at all times, where as an aeroplane can be flown without APM. (manual)
I know I wandered a little off topic, Hope this helps.