I’d just give it a whirl, k. Impedance mismatch loss is relatively small as long as the mismatch is not astronomical, and most receivers (including the RSP’s) have gain to spare anyway. A quick look at at that diagram doesn’t show any danger from DC supplies leaking into your RSP’s front end or anything like that, so I’d say go ahead and see how it goes.
BTW, this forum is now independently-run and has no direct connection with the SDRPlay guys any more, so it is very quiet.
For a *lot* more action try joining the Facebook community, it’s very friendly. There’s a link on the main Play homepage.