Upgrading System

[Snpbond]

Hey all, I am a bit confused at all of this audio stuff, I have tried to research it as much as I can and this is what I am thinking.

Right now I have an old Sony system (HT-DDW670), which is a 5.1 system with a reciever. Now I am wanting to upgrade to a newer system to utilize the PCM audio. My questions are:

1) If I were to upgrade my reciever to a new sony one (the new ones that are coming out this year such as the STR-DG820), could I still use my current speakers (6ohms, and as far as I can tell are 100 watt speakers, the current reciever outputs 100 watts per channel). The new recievers output 110 watts I think, and have 8ohms output but can be changed to 4 ohms I think, would thatsupport my current speakers?

If I went this way I would eventually buy new speakers so I could have 5.1, but Im on a budget.

Next,

2) I see on sony's site right now that certain recievers do Linear PCM but not all do the Dolby Digital True HD or DTS-HD, whats the main difference? Do I need to get the ones that do DTS-HD?

3) What recievers would you recommend, I've looked at Onkyo's and Yamaha's but I would need new speakers and I'm on a tight budget being 17 going on 18 years old

Thanks for the answers


--Edit--
I dont know if its relevent but I use a PS3 for my blu ray watching, I've read that it converts everything to PCM anyways..