Received my 1050 today and thought I am using it in Stereo Mode the Sub indicator on display is lit.

How can I disable the Sub?

Set your front speakers to large.

Also, try the different crossover settings the 1050 has to offer. You may discover one you like better than just listening to your mains. Also, try using just the 5.1 direct inputs if you want to use just your L/R speakers.

I believe you can turn the sub off with the round button under the channel up/down buttons on your remote. It should be labeled 'SPKR', I think.
As you press it, it will cycle through all the speakers and give you the choice of small, large and the sub, on or off.
Try this or (more wisely) check the manual, page 21. It's on the Outlaw website as an Adobe document.

I know getting a new 1050 is too exciting to take the time to read the manual but I really suggest you do. I cheated by downloading the manual before my 1050 arrived so I could read it undistracted.

There are a lot of setup instructions you will want to read so you can get the best performance out of your 1050. Pages 21 and 22 address the speaker configuration. You probably don't want to set your front speakers to large unless you have speakers that are capable of extended low-frequency response without distortion. Most speakers are best set to small and then set your cross over to a setting that is as low as your speakers can handle or to a higher setting if your tastes prefer.

Outlaw has one of the best manuals for electronics I have ever read. Clear well spoken descriptions of not only how to change the optional settings but also what the settings do and why you want to set them.

Then turn up the 1050 and enjoy !