I'm not sure that thing about the poo is about wanting to show disrespect or not having been taught correctly. When similar things have happened in the Cory household it has been at very stressful times (and heaven help us, we've had a few!). Same with drawing on walls (once they had got beyond the age where you'd expect it).
I wonder if there might be something in what Littlefish says, that you may all have got into a rut of negative feelings. There is nothing more difficult to handle than a little boy who feels he is naughty anyway, so it isn't really going to matter what he does.
I would not resort to crying for effect at this time- it may weaken you as a disciplinary force or make them feel even less convinced that they can be good.
Instead I would start at one end. Make a list of a few problems that you think could be fairly easily tackled- like the ds games and the dvd's. Do as Littlefish suggested and have a planning meeting and agree sanctions; which you then stick to! Make sure all punishment is swift and immediate and relatively short-termed.
And try to make it a rule that the sun does not go down on your wrath- a new day means a new start. Doesn't mean that you have to give back confiscated goods, but it does mean that you have to start again speaking to them as if you expected them to be a source of pleasure to you. Every morning, whatever happens later in the day. You need to move on.
As for pulling clothes out, was it perhaps part of an imaginative game? (Dd's bedclothes were all over the floor at the end of her sleepover with her friend). Not that you should allow it, but it will make you happier if you don't feel they were doing it deliberately to hurt you. If you see some sort of sense, it will also affect the way you speak to them about not doing it again iyswim.
As for breakfast, could you maybe eat it with them? There was another thread on here recently where the majority of posters said they really wanted to get up with their teenagers in the morning, to be there if they wanted to chat or whatever- perhaps this would be a good idea for yours too?
Also, are you all able to have enough fun together? I don't necessarily mean big expensive fun like a day out or anything, just little things like sharing a book or having an interesting discussion about something. I do find the more shared moments you have, the easier it becomes to move on when something has gone wrong.
I am not averse to (metaphorical) whip-cracking myself, but it's all about balance.