Cart before the horse or horse before the cart?

What do you currently own?

Personally, I would suggest getting the least expensive receiver that you can that includes pre-out for all channels. This will give you the option to combine it with a dedicated 2 channel amplifier in the future for the best music listening. I think "requirement" might put you in the $800 range for a new item. Speakers don't get dated when it comes to technology, but receivers can. You want one that will handle all of the lossless blu-ray audio formats and HDMI 1.4 that will do 3D TV just to be current with technology.

You'll want to plan for a subwoofer to make a 2.1 home theater for the best sound.

Something similar to a Pioneer VSX-1120-K would be a great unit as it's very current with the latest technology.

If you're not wanting the option of pre-outs to step in the future to a 2 channel amplifier then you can drop several levels down in that same line and get a VSX 820 that should have plenty of features for less money. A friend of mine recently purchased this model for his 2nd system. He uses a Pioneer Elite model in his home theater room and used the 820 to run the rest of the speakers in his house.

Onkyo and Denon are also great options, I prefer Onkyo over Denon simply because they are a bit more user friendly with individual buttons on the front rather than a spin selector knob.

In my opinion, the two most limiting features in a receiver in the long run is not having pre-outs or 4 ohm capability. Both of these features add to the cost so you need to figure out how much it matters to you.

I also don't think that in the price range you're looking at that matching speaker and receivers is as critical as it obviously is in the higher end gear. I don't think the difference between a Marantz, Denon, Onkyo or Pioneer will make a significant difference with any speakers you'll be considering.

Onkyo TX-NR808 would be a great option from the online retailer that you speak of. A co-worker of mine just purchased one and seems very happy with it.

It is rated for 4 ohms and has pre-outs. The current price is right in your range.

As far as I know, the 3D feature is just the latest HDMI connection. I don't think there are any specific features built into the receiver itself.

The TX-NR708 has all the same features with less rated power per channel but still maintains pre-outs and 4 ohm performance I believe.

Unless the price difference is significant for you, I'd get the 808.

To answer your question, the previous year TX-NR807 wouldn't have 3D capability, but the majority of current models will have the latest in HDMI technology and that means 3D capability.

Another co-worked just purchased the 2nd to the lower Pioneer in the line I previously recommended to you and it was 3D capable for under $300. I believe the most entry level Pioneer is 3D capable.

Personally, I like the idea of being as current as possible with receivers as you never know where technology will go next.

A little more information to help you in your decision.

My previous receiver was an Onkyo TX-SR606 that was rated for 90 wpc and continuous 6 ohms performance. My new receiver is an Integra 50.1 that is rated for 135 wpc and continuous 4 ohm performance. The improvement in sound quality was dramatic. I don't know how much to attribute to Integra vs. Onkyo, 135 vs 90 wpc or 6 vs 4 ohms, but the spec differences are similar between the 708 and 808 that you are comparing. The difference is that both are 4 ohm receivers.