gaderson,
I still have my SP-1 remote from when my SP-1.7 was an SP-1. It seems to operate my SP-1.7 with no problems, except for some of the new features are missing. As far as I can tell, the SP-1 remote has no "CODE" button like the SP-1.7 remote does, so what you see is what you get with the SP-1 remote. BTW I really liked the SP-1 remote's membrane buttons and simplicity.
I looked at the HDS4.2 website. It looks like your are out of luck with the RS-232 control (unless a computer or device with 2 serial ports and sofware is inserted between the SP-1 and HDS4.2) but the webite says that the unit will learn the codes of a remote. I'm not sure exactly how the codes are assigned to the operations of the HDS4.2 because the link for the user manual is the same as the brochure link.
I would be more tempted to purchase an SPV depending on the number of video inputs that you require, and whether you have more audio inputs than provided by the SP-1.
The Iscan is a different choice because of its scaler functions, however, I imagine that it could be used with the SPV to get OSD, scaling, and switching.