I use Digital Video Essential. I find it very useful. There's a complete battery of audio and video tests including Dolby 6.1 sound tests.
It also has tons and tons of information about speaker and sub placement, sound processing, video processing, etc, etc. Very interesting stuff.
Three remarks though.: 1- Its more expensive than Avia, about 10-15$ (if i'm not mistaken) 2- It has a bunch of tests with no explications (geared for the pros) 3- The DVD menu is a total pain, never seen worst.
Now. I never saw Avia, but I've read a lot about it. If I were to choose again, I might pick up Avia first (if it has 6.1 tests, of course)
I definitely recommend you pick it up. Its a very small investment, relatively to the cost of your equipment, that could make a significant impact.