Cannot do 5.1 then does 3.1 make a difference or just stick to 2.1?

Does center channel make a difference when I cannot have anything more than a 3.1/3.2 setup?.
The front mains are Legacy Aeris and I just do not have space for Legacy marquis XD it is 14" in height just a bit much. I have to change the AV cabinet for that to work. Can I just live with the front mains and a sub for both music and movies?.
Your AV processor should give you options for defining how many speakers you're using and will distribute the sound accordingly.  You should be OK with 2.1. 

What you can "live with" is up to you.  I am old enough to remember the days where having two speakers on the TV itself was audio nirvana :)  We are spoiled with all the options we have available to us.

The center channel is where most dialogue comes from and when listening to movies it will help make the dialogue more clear and obviously have it be coming from right in front of you. 

Legacy has a smaller center channel speaker, the Cinema HD.  Have you looked at that?

Many would recommend against this because of "timbre matching", but you could also consider another brand of speaker that would fit in your space.  My home theater setup is a mix of Legacy Focus 20/20 for mains and Klipsch speakers for surrounds and center.  I find the Klipsch RC-7 works fine (for me) with the Focus 20/20s.  My ears are not "golden" enough to hear any integration issues between the Klipsch and Legacy speakers.  I have space issues of my own and the RC-7 is bigger and more efficient than the Cinema HD and fits in my space.
It's not too terribly bad to live with a 2.1 system, as long as you know the shortcomings.  Essentially, like big_greg said, the vocals from movies will be a lot clearer if you have a dedicated center channel.  There is a bigger reason why this is. 

In pretty much all movies, voices and certain movie sounds are mixed directly to the center channel.   However, on many movies, the left/right speakers are used to provide "ambient reverberation" of the voices tracked to the center speaker.  Sometimes this is based from real room microphones, but often the voice is ran through a delay/reverberation effect unit and then sent to left/right (to provide echo of voices in a room, for example).  This center + left/right mix gives your ears a better definition of the voices.  In some movies, the surround speakers are further used to extend that "room reverberation echo".
If you just use 2.1 with only left/right speaker, your AVR or HT Processor can handle this, but the center channel sound is split and sent to the left/right, also along with the original left/right reverberation sounds.  Because of this, with some movies, the voices and sounds could seem to have a weird echo and it can be harder to understand the voices in some movies because the source of the voice is no longer starting from the center channel and naturally extending to the left/right and the surrounds.
Thanks big_greg. Much appreciate your input.
I agree with big_greg that you could look at the Legacy Cinema HD.  If money is not an issue and 10" is not too high, I would probably look at the Legacy Silverscreen HD instead, to keep the ribbon tweeter voicing that would match your Aeris. 

I don't know that I would recommend the Klipsch RC-7 because the horn-loaded tweeter is going to have a radically different voicing.   If you are going to look at different brands, I would look at a Dali Epicon Vokal first, because it uses a similar AMT ribbon tweeter and I think the voicing will be a lot closer than Klipsch.   However, the Legacy Silverscreen is still going to be the best.
Thanks all I decided to get the center channel and going all the way. Need to fix furniture later. Thanks again
My two cents: Center for movies with your setup. Music, keep it two channel for your setup.