RG6 *IS* the standard cable for DSS. RG59 is *substandard*. RG59 is not recommended. Use it at your own risk of headache and frustration.
It may "work," but expect the following: Lower signal levels, which translates to longer-lasting more frequent rain fade (loss of signal) , possible occasional loss of half of the channels (loss of polarity switcing at the LNB), and less likely to expand the system beyond two/four receivers because the components to expand the port count further reduce the signal levels.
RG59 has much more loss and much less DC voltage carrying capability (power to the LNB is through the coax from the receiver +13VDC and +18VDC). RG59 is almost double the loss for each.
You CANNOT, CANNOT, CANNOT use any kind of splitter between the dish and the receivers (a multiswitch is not a splitter). Not even the ones with little pictures of satellites on them. They are for splitting the RF (TV out) output of the receiver ONLY.
If you try using a switchbox, make your choice wisely, some will ground the "off" port, which will smoke your receiver.
If your installer says RG59 is OK, and doesn't warn you that it's not recommended, send him home, get a different installer.
Get it done right, you'll be a much happier couch potato.
FWIW
Scott