Listening to DTS-HD & TrueHD with only 2 Speakers?

I only have 2 speakers and no HDMI inputs on my preamp. Will i still benefit in "night and day" improved audio quality when watching a Blu-ray over watching the same movie on DVD (both still with only 2 speakers)?

Or do i need to purchase 3 more speakers (3 ICs, and 3 speaker cables) to truly realize the benefits of Lossless HD codecs?

Hard to say. There will definitely be an improvement in detail and transparency but how significant it will be to you, I cannot predict.

I think you should be able to hear the difference. I am not sure about "night and day" though. DTS-HD and TrueHD suppose to be lossless while DVD is compressed.
I agree with Kal, having gone through this. I then picked up an Integra 9.8 processor (HDMI ins and outs) to go with my Sony blue-ray player. With 5 speakers and after some initial configuration issues, I've gotten much better sound than I would have thought possible for movies - literally just like at the movies (but no bathroom or snackbar lines!).

In other words, there is amazing hidden audio capability with these new formats that can be pretty easily tapped with a little guidance. Good luck.