I recently upgraded the Plex Media Player version on my HTPC and Plexamp can no longer fling content to the HTPC from Plexamp.
Plexamp has no issues playing content from the PMS, however under the Player sub-menu in PlexAmp only “local” is listed. I had previously been using an older version of PMP on the HTPC and had no issues flinging content.
On the same machine running PlexAMP, the PMP instance has no problem seeing the other PMP instance and flinging content to it.
Plexamp version 1.1.0
Plex Media Player version 2.28.0.952-5408ca22 (Windows 10)
Plex Media Server Version 1.15.1.707 (FreeNAS Jail)