I'm just a music consumer (with a pair of 305's) who's been casually following this out of curiosity, but I just felt I had to chime in...
What I'm reading here is that Ianpb has bought the tool but not set up his workspace, then found he can't get the result he's after. It's like trying to saw wood without clamping it down; however many saws you go through, you're going to have a hard time getting a good, straight cut.
Unlike my analogy there, however, acoustics aren't nearly so obvious if you're coming from a place of ignorance -- if you don't know how all those little soundwave bounce around a room, you're not going to notice that you've got all the wrong surfaces in all the wrong places, and will tend to assume it's something you do see. Point being that it's an easy mistake to make for someone who's new to setting up a studio (home or otherwise).
Now, I can certainly see how the computer speakers apparently sounding better would suggest the monitors are at fault... but my understanding is that the chief difference between [high-end] media systems and studio gear is that the latter assume everything -room, listening position, power, etcetera- is set up optimally, while the former has to be much more flexible in terms of where you can get a good experience. A family isn't going to have much use for a system that makes movies sound awesome... but only if you're sitting in one specific spot.
So what I suggest has happened is that Ianpb has gone from something designed for the sort of space he's got it in to something designed for an entirely different arrangement, and hasn't made the appropriate changes. Some personal preference may also be mixed in, and other hardware (or software) in the chain could be affecting things, too.
My suggestion would be to do some homework about acoustics and room treatment, do what can be done, and then experiment with different speakers. Getting that stuff right will pay off regardless of the monitors one likes.
(But I'll be not the slightest bit offended if people tell me I have no idea of what I'm talking about :P.)