I know this has come up before but I'm having trouble finding references. It might be have been in a live conversation with one of the Outback folks.
I am interested in this because the PV system I have in my first house is exactly the configuration that you mentioned SW5548 (dual) and 6 SB3048s.
I can "watch" the SBs work during the day (fortunately I normally watched TV using a satellite setup). I originally left the covers off of the SBs (they were inside Trace Power module boxes) but I ended up putting the covers back on to try miminize radiated RF.
I also discovered one of the doors to the power module boxes was not making contact so I fixed that and made sure the box was grounded all the way around.
I believe I was still left with conducted RFI but I haven't had a chance to track it down. I don't live in that house anymore and my tenant has complained so far :-)
Anyway one of the reasons I'm interested in the Outback is to reduce the amount of work I have to do to mitigate RFI. What I can recall about Outback is they indicated that they should have better RFI performance. The MX60 designer is apparently a ham radio operator so he has a strong interest in keeping RFI down.
I also read they there were looking into an "external fix" (filter?) for some RFI problem with the FX-2000 (ah, found the reference:
http://www.outbackpower.com/cgi-bin/Forum/ultimatebb.cgi?ubb=get_topic;f=10;t=000016).
arnold