Is there any way of restricting a DVB device within vdr so that it will never record more than one channel from the same mux/transponder?

I have acquired a Nova-T USB second-hand, as in a USB 1.1 device which struggles to even stream one channel at a time. If there are concurrent recordings on this device from two different channels, they are both totally destroyed due to the lack of bandwidth! Just one channel is bearable, although still quite crap, so it would be good to be able to set a given device so that it will only ever do one recording at once. Is this at all possible currently?

Does anyone have an experience of the newer Nova-t USB2 devices? Do they work reliably and for several channels at once? This is as an additional device for an Epia system with a single PCI slot :-s

Cheers,

Laz