Factory sub or not?

I have a 2006 Hyundai Azera with the factory Infinity system to include center channel speaker in the dash, tweets high on the front doors, mid drivers low in the front doors, coaxials in the rear doors and a sub mounted in the rear deck.  According to the folks at Infinity...the front center is crossed at 200 Hz (hi), the door speakers are crossed at 60 Hz (hi) and the sub is crossed at 80 Hz (low). 

I have replaced the door speakers with Infinity Kappa 6.27i's and I added an external amp (Phoenix Gold 600.1) to run a sub (Phoenix Gold Xenon 10D2) I installed in the trunk (mounted inverted firing into a sealed box). 

My question is...should I keep the factory sub active and cross the new sub down around 50 Hz, or should I disconnect the factory sub and cross the new sub at 80 Hz or maybe even 100 Hz??? 

Mike

Thanks for the input fellas.  I ended up trying it both ways and this is what I got.

With the factory sub disconnected, I set the PG amp at about 100 Hz.  The fact that the amp is pushing 600 watts, it overpowered the factory amp and the sound wasn't smooth.

With the factory sub connected, I set the PG amp at around 50 Hz and the subsonic filter for 17 Hz and let me tell you...the transition of sound from front to back is almost seamless.  The higher bass frequencies come through nicely on the factory sub and the PG sub/amp push out the lower frequencies for that deep rumble that was missing.

However, now I'm considering replacing the factory sub with an aftermarket one, but we'll see.

Again, thanks for your feedback.

Yeah...I toyed with it and change the settings.  I think one problem is the fact I had to use a hi/lo converter to get the signal to the amp since I still have the factory head unit.  So that signal isn't as clean nor does it adjust as well as it would a direct RCA connect from the head unit.

Anyway...using it to belt out the sub-bass...is working very nicely.  It blends nicely with the factory sub and gives me plenty of bottom end without overwhelming the rest of the system.