The BX3000T, now replaced by the BX4500H and the MAG 300
are entirely different animals. Only looking similar from the outside. I own a MAG 300 and a BX4500H and both have their merits. The MAG 300 is a better design technically and probably sounds better too. The BX4500H is an upgraded BX3000T and is VERY similar.
Can't comment on sound for the BX3000T but I expect it's much the same as the BX4500H lacking some definition but has TONS of power and balls, the preamp section, you can bet, is identical. The MAG 300 has a far better designed preamp, is quiet and the 'ultrabass' feature works better too although I think it's a crap feature.
I don't think you'll be that dissapointed with either. if you go for the BX4500H instead some suffer very noisy preamps so be warned.