2.1 system for home theater

I believe that dialogue issues in 2.1 setups are generally the result of one or number of things:

1) Flat Frequency Response: The speakers don't have a linear response in the room. Nulls and Modes can cause the tonality of voices to be off enough that it doesn't sound right and is thus difficult to hear.

2) Imaging: Hearing clear dialogue from a 2-channel config is highly dependent on proper imaging of a phantom center as well as an even response so that the image remains consistent across all frequencies. It's critical to make sure the speakers are optimally placed in the room for staging an frequency response.

3) Insufficient power: It's really important to properly drive your speakers with a good amp. Many receivers are incapable of sufficiently driving demanding speakers. I see a lot of blame placed on speaker issues when the problem is often that the speakers aren't given enough/clean/consistent power.

4) Room correction: Run room correction a few times to make sure you're getting the most out of it. Ideally use really good room correction like Dirac Live, Audyssey MultEQ XT32, or ARC Genesis. Avoid mediocre room correction (pretty much anything else other than the really high end stuff). Also, I've found that dialogue ineligibility can be cleared up when using Audyssey sometimes by using the Mobile App to disable MRC (mid-range compensation); totally depends on the speaker though.

5) DAC: This one isn't discussed enough, but the DACs in many AVRs aren't as good as they could be. This becomes really clear (pun intended) if you get the chance to experience the difference between a typical AVR DAC and a high-end DAC. The best receivers & pre/pros tend to have better DACs.

6) Speakers: Some stereo speakers just don't do a great job with voices. You could plug one of your L/R speakers into the Center output on your receiver to test this.

7) Crossover: It's a good idea to play with the crossover between your subs and L/R speakers to see if this can help with clarity. You should ideally have your crossover set between 60hz to 80hz, but sometimes its worth going as high as 120hz if your L/R speakers can't produce clean bass and if your sub is really good and is in a responsible location for frequencies that high. Also, it's important to only have one crossover for your sub so make sure that your sub's own crossover is disabled if it has one.

8) Time alignment: Check that your speakers are set to the correct distances on your processor and test with music to make sure that the imaging is correct as a result.

With all that said... the reason a center channel is often the easiest path to clear dialogue is simply due to the fact that you're moving the voices to a nearly dedicated speaker that doesn't have to also playback all the special effects, background noises, and soundtrack... it's just less demands on the speaker where the voices are coming from. Less demands on a speaker means that it is less strained and that the items I mentioned above are less likely to be audible.

I used a 2-channel setup for years to watch movies and was more than happy with it. With that said, a great center channel is always a good idea, but I prefer to not use a center channel as a band-aid.