To answer your question in very general terms, separates are usually advised to provide a cleaner sound to your speakers.

Why?

Well, as you crank up the decibel level, you are placing a larger and large demand on your amplifier. To keep distortion to a minimum, you want to use only a relatively small portion of that power so that you are staying in a range that is fairly linear in distortion and very low. The harder you work an amp, the more distortion you will introduce, especially at its higher limits.

Again, a VERY general explanation to your question.

If you have to turn your receiver up past half way most of the time you are listening to music or tv, you may very well benefit from a cleaner sound provided by a more powerful amp. Again, this is a very general guideline. Some receivers provide a VERY clean signal and plenty of power for some speaker designs that are very efficient and have high sensitivity levels.

I hope this answers your question.

P.S. I am not familiar with your receiver but if it has pre outs, it should support a separate amp. You should find this info in your manual.