If people are gonna say XXX cube is crap, then I'm gonna say Type B's are the best.
Point being, stop saying cubes are crap. They can be awesome to other peoples.
On Topic:
Don't loosen the tensions. Stupid idea. It's just going to lock up more. The cube performs best at tight tensions. Corner cutting isn't one of it's strong points, and it never will be, so loose the idea of loosening the tensions. Lube with Jig-A-Loo, then optionally, Maru lube, and it will be great.
Make sure all the tensions are even, this is a must, especially on a cube like this, because it's very sensitive to tensioning. It should be even to at least an eighth of a turn, but it should be to a sixteenth.
A5 mod, or rounding the corners should help, but I don't recommend it. If you already did that, you might as well round the edges too.