Samsung 34" S34E790C monitor 3440x1440 not working with Mac Mini (Late 2012)

I have the Mac Mini (Late 2012) i7 2.6Ghz with 16GB RAM. Running latest version of Sierra.

Since there is only one Thunderbolt port on the Mac Mini, I'm using this to connect to an 8-bay HighPoint RS6618T NAS. I then daisy-chain from the NAS's thunderbolt port to my Samsung S34E790C monitor's DisplayPort. I have a Thunderbolt to DisplayPort cable. I can get the monitor to work at 3440x1440 resolution at 50Hz. Great!

Here are the problems I'm having:

• If I walk away from the computer, the monitor never goes to sleep, even though I have the setting turned on.
• I need to turn the monitor off via the power button. Not a big deal. If I come back later on, I may not be able to get display again until I turn the Mac off and back on again by shutting the Mac Mini off manually.
• Sometimes the screen is all garbled and I need to bring the resolution down to 2560x1080, and then I can go back up and it will be fine.

Any help would be appreciated! If I can't get this to work, I may need to either return the Mac or figure out a different monitor.

I really like the 3440x1440 resolution, as it's ideal for my size monitor. I do not want to have to give it up.