I have the update (4090) and it's still not fixed for me. I've got the Roku Ultra and I'm using optical out for audio. Are you guys using the same setup?
Just adding to the chorus -- I've got one of the new TCL 6-series Roku TVs (55R615) and am also experiencing sync issues with DTS audio. The audio is ahead of the video; not exactly sure by how much, but it's enough to be obvious. If I had to guess, I'd say maybe 100-150ms?
TV is connected via S/PDIF to Pioneer VSX-815 receiver (older 7.1 receiver circa 2005/2006, but handles only vanilla 5.1 DD/DTS signals, no HD formats).
TV software is on version 8.0.2; I'm 99% sure the build number is 4133.
So far I've only tested a couple of MKV's containing DTS 5.1 audio tracks, played via the Plex channel from my local Plex server. The files were Direct Played, no transcoding. Playing the exact same files on the computer with e.g. VLC player, the audio sync is just fine. If I change the Roku TV settings to disable DTS via S/PDIF, then Plex transcodes the audio to DD 5.1 which is passed through to the receiver and sync is perfect.
I'm going to try putting a couple of these MKVs on a USB drive and play them directly via RMP, though I don't expect any different results. I'll also try a Blu-Ray with a DTS soundtrack connected via an HDMI input. Are there any streaming channels where I could test some streaming content with a DTS 5.1 soundtrack?
I see the release notes for Roku OS 8.1 mention "Improves support on Roku TV for DTS passthrough from HDMI inputs to AV receivers and soundbars." Any chance that A) means Roku has fixed the DTS sync issue, B) it applies to passthrough to both HDMI/ARC and S/PDIF, and C) it will also fix it for audio sourced from a channel (e.g. Plex), rather than an external device connected via HDMI?