'04 Vibe GT stereo

Hello: I've got a few questions.  A little background:  I've got an '04 Vibe GT w/ a moons and tunes packaage( That means that there is an external amp)  Now I've ordered a new component set of speakers that says it can handle about 75w RMS and then another set of Speakers rated at 70w RMS.   I was wondering:

1. Is it possible to power one set of speaks with a new headunit (Sony CDX-M850MP that's got 3 preamp outs) and the other set with the external amp?

2. How would I do that?

You should be able to use the existing amp from a preamp out on the new head unit.  Normally the preamp outputs work in addition to the speaker outs, so hook the speakers you want the head unit to power to the speaker outs on the Sony, then use one of the preamp outs to feed the power amp and run its output to whatever speakers you like.

You might benefit from putting larger diameter / lower frequency speakers on the external amp, particularly if your head unit has a control for a subwoofer. 

I don't know your head unit, but sometimes a subwoofer active button changes the frequencies sent to the internal amp... this helps to better share the work of making sound.  Low frequencies require the most power - a good rule of thumb is 3 times the wattage for low end as compared to the midrange... but then subs require even more power than low end!

There!  My two cents and my first post in the forum...

Regards,

Wolfgang