[TenTec] Orion hookup questions

[N3SL at aol.com]

I received my Orion last week, and I'm now at the point of hooking  
everything together.
I have a general question for those more expert than I:
I'll be running the Orion with an Alpha 91B, which has the "key loop"  
circuitry.  With my 1000MP, all I've ever used was the keying  transistor in the rig 
to the relay input of the amp, and things  always worked fine.  Is there any 
particular advantage to using the  key loop (TX OUT/TX EN) circuit vs just the 
AMP KEY, which I'm presuming is  just a transistor output?
On a more "rhetorical note" - Anyone know why TenTec supplies an accessory  
cable that's only 5 pins, so doesn't include something as basic a FSK  
connection, but does include the pin that's a spare?!  I fail to see the  
logic/purpose in that.
Thanks in advance for replies.
73,
Steve