Have 6 channel amp what's next ?

There are some options for you but first things first. You have a 6 channel amp and want 5.1 so assumeing you use a powered sub you will only have 1 extra channel for multi zone use, thats one issue you need to understand.
You could get a another cheap used 2 channel amp so you free up those channels for multi zone on your Pre/Pro, so yes you do want HT Processor, Rotel, Emotiva, Outlaw, and a few others will be in that budget but its gonna be very limited with your desore for HDMI. Emotiva is at some point soon bringing out a Processor that would be perfect for you but its been delayed, you dont need HDMI unless you really want the new HD audio formats that are very limited in release, choosing instead a unit that runs Component (red, green, blue) video may make more sense financially and run seperate digital audio feeding the HDMI direct to monitor for best picture. You dont mention speakers so do you need to buy those and sub or did you just not give that info? If speakers need to be looked into then forget HDMI in you Processor for that amount.
I will PM you if you want to call maybe I can help with some questions. cheers and Happy Thanksgiving

I have an inexpensive 2-ch amp for the 2nd zone and in regard to speakers I have in wall fronts, a B&W Matrix for the center and in ceiling rears already installed and ready to be connected. I have a sunfire powered sub as well. I just figured that for the best Picture/Audio I should use HDMI 1.3.
Is this not correct ?

Yes and no, if the Plasma is 1080p and you intend to watch many Bluray movies then HDMI either into a Processor (like Emotiva mentioned) or you can go straight HDMI from disc player, Satelite and Tivo (make sure you have enough inputs) into Plasma direct then you would go Digital Coax or Toslink wire for audio into the Processor if it doesnt have HDMI, the only thing you will loose is the most advanced HD audio on Bluray discs only as Satelite at this point doesnt support these formats. You can also go multi channel RCA inouts from a Bluray player with a built in decoder and get the HD audio with need for HDMI circuits.
The bottom line is budget, if you cant swing a HDMI processor its not the end of the world and you have options to get around that. I did send a private message if you want some more info.

If you can bi-wire/bi-amp your center channel, that would be awesome. Otherwise, the 6th channel will not be used. Make sure that you don't have a signal into it if it's not hooked up to a speaker.
You will have to get a pre/pro with or without a tuner. If you are new at this, go with a more simple unit if possible. Get a remote that doesn't take a computer tech. I really like sunfire/sherbourne/anthem.
For zone 2: Most pre/pro's will run a second zone. However, using the same unit for this will make things more complicated. Plus, you will need remote IR emitters and such. If you are a novice, either use a completely separate second zone or pay a shop to set it up. I'd suggest selling your second amp and buying a multizone receiver like Denon 385.

You could use extra channel for 6.1 for more spacious ambient surround or I have used an extra channel for bass shakers installed in seating.