I could not find a lot of info on the DEH-P300 or the Orion amp. The jensen amp puts out 300w bridged, and the other two head units are about the same. I think I would go with the Panasonic. But you might want to do a little research and see which one has the features you like. As far as your system and what I and all others will suggest, we all have our own preferences. Me, I love JL Audio amps subs and their top of the line components. I also like the Boston acoustic Z-6. First off, I would lose both amps and go with the JL 5 channel amps. It's a matched set, it's one amp, and puts out great clean power. I have this.
http://www.dealercostcaraudio.com/jlaudio5005rb.aspx In my truck I'm going to go with this one though.
http://mobile.jlaudio.com/products_amps.php?amp_id=537 i don't think you need the second amp. For the music you listen to the first will be fine. I would also go with a JL Audio 10 or 12w3.
http://mobile.jlaudio.com/products_s...p?series_id=24 I have the 10 with the above mentioned amp. As far as the component sets I'd go with two sets of these.
http://mobile.jlaudio.com/products_c...php?comp_id=65 Like I said before I'm partial to JL Audio. And ten dif people will suggest ten dif brands. As for the speakers. You should really go to a stereo shop and listen to all they have and go with what sounds best to you. Ask how they have them hooked up and what they are hooked up to. That will change how they sound when you hook them up in your truck. You also don't have to buy them from that stereo shop. There are a lot of online stereo shops that are a lot cheaper. Just make sure that they are authorized dealers for what they are selling and what the return/warranty policies are. And there is a lot of good info here.
http://www.fullsizechevy.com/forums/...o-electronics/ I'm sure by now you are tired of reading my ramblings. Hope all of this helps in your decisions. If you have any more questions feel free to ask.
Dale