The proposed solution does not work. I have two Slingbox 500's and a M2, as well as 3 Roku devices from the stick to top of the line. All became inoperable within a couple hours last night (Sept 23, 2019) while in use with Slingplayer. I found the Google Chromecast had no problem with streaming the Slingplayer, which is the sole reason I bought the Roku. I put the Roku in the desk drawer and plan to purchase 2 more Chromecast units and perhaps an Apple Fire stick to see what it's like.
Alternative Solution: Use a Chromecast for Slingplayer.
Roku Customer Support
james, Sep 24, 17:28 PDT:
Chat started: 2019-09-25 12:22 AM UTC
(12:22:07 AM) james: why did slingplayer quit working
(12:22:10 AM) *** Manaz joined the chat ***
(12:22:16 AM) Manaz: Hello James!
(12:22:18 AM) Manaz: Thank you for contacting Roku Support!
(12:22:50 AM) Manaz: I understand that you are inquiring about Sling player channel.
(12:23:23 AM) james: yes
(12:24:07 AM) james: sling player was the main reason I got a roku
(12:24:59 AM) Manaz: Let me check.
(12:27:16 AM) Manaz: Please be informed that, the Sling player channel has been removed from the Roku platform by the channel provider.
For more information, you can contact the channel provider regarding this.
(12:27:18 AM) Manaz: http://support.slingbox.com/contact
(12:27:27 AM) Manaz: Please visit the above link.
(12:27:56 AM) james: thank you
(12:28:24 AM) Manaz: You are welcome!
(12:28:25 AM) Manaz: Have we covered everything that you wanted to discuss?
(12:28:31 AM) james: yes
I have been using my Slingbox with an iPad for nine years. Before I got my Roku, I connected my iPad to my TV with a cable. You need an (overpriced, Apple-only) iPad-to-HDMI adapter (Lightning to HDMI in my case) and a sufficiently long HDMI cable to reach the TV from the iPad. You use the iPad Slingplayer app as before, and the TV mirrors the iPad screen. (This setup mirrors any iPad app!) You might have to fiddle with the aspect ratio setting on your TV to get a full-screen display. I had to set my TV to "Full Zoom".
I was quite excited when I got a Roku and discovered the Slingplayer channel. I'm disappointed that I have to revert to the wired connection, but I can at least continue to view my Slingbox on my TV.
I don't have a similar wired solution for Android devices.