The tiger barbs dont distrub the discus really...they mostly will hide in spaces you give them. Never had a problem with them nor have I ever heard from people of any problems with them in a discus tank. They might get a little hyperactive from time to time....but that's about it.
Even with "good" w/c's....the presence of gravel will create a problem later down the road. Even if you are able to totally clean the gravel every week...there is still a huge risk factor because the gravel will harbor bacteria. Discus need a fairly sterile tank in order to remain healthy and growing well. This is why people suggest bare bottom tanks. With the gravel in the tank, it is basically a time bomb waiting to go off because the older the tank gets, the more bacteria gets established in it. With a bare bottom tank you are able to keep the tank MUCH cleaner...and the fish will remain MUCH healthier. Discus are not ordinary fish with ordinary requirements...they require a bit more specific needs and a bit more attention...which is why there is so much false info out there such as discus needing things such as a certain pH level...this is 100% false. Discus can adapt to almost any pH level and live happily. If you want to keep discus successfully, the secret is to maintain the water quality. The more w/c's you are able to do, the better. You will be able to tell a difference in the way the discus act before and after a w/c. They are MUCH more active and much happier right after a w/c. But with w/c's on a weekly basis, there is a huge possibility for them to become stunted and not reach their full 6-7"+ size range. Anyone here ever see a 10" discus? I have. A fish that size was only created by keeping the tank clean at all times with multiple daily w/c's. That and feeding a complete diet consisting of Beef, Shrimp and fish will they be able to reach such a large size.
Ok, sorry...went off on a tangent there....
Anyways...if you want your first discus experience to go over well, then i suggest bare bottom tanks. If you want it a bit decorated, then add in potted plants with a piece of drift wood or two. Just make sure that the bottom of the tank is bare, with the exception of the potted plants and driftwood. Hook up a wet/dry to the tank to filter it. Make sure the temp stays in the mid 80's with a good, reliable heater...and above all else...do as many w/c's as you possibly can. If you slack on them, the discus will let you know by hiding, not eating, becoming dark, skittish, getting sick, etc... keep up on the w/c's and they will come to the front of the tank to greet you and even feed from your hand. Following these simple guidelines will let you have a good discus experience. Oh, I also suggest joining one of the two major online discus forums:
www.discusasahobby.com
www.simplydiscus.com/forum
There is a wealth of info on those two sites alone, along with even more people to help you along the way. Discus are not nearly as hard as everyone says they are. Its just that some people are ignorant enough to still believe in old skool info and pass that false info on to other people. The more you know about discus, the easier they become to have in your tanks.
-Ryan