I love my Magnum 350! Never fails on me and I have more than one. None of them failed on me ever either. The room for types of media is not the best, in fact they only have one container for one type of media but they are still a great filter IMO.
One thing, what do you mean by they are not enough? What problems are you having? Is it mechanical filtration?
If so I would even be happy with what you have and a HOT Magnum. Simply use the HOT Magnum with its Micron filter and gravel vac attachment to do some polishing via gravel vacing and after you are done, if the flow is still good just leave it running with the gravel vac off and diffuser back on as a standard hang on water polisher.