Hiya Daniel
I have bad news..
Your Asus is really absolute basement.. bottom of the barrel model. Mediatek rubbish..
It is really important to understand what you buy.. when you buy it.
See the specs.. I did a quick google..
ASUS RT-AC51U Specs - CNET
And a site that tells you the more indepth info.
https://wikidevi.com/wiki/ASUS_RT-AC51U
So.. point number 1. The Asus does not have gigabit ports.. only fast ethernet.. ie 100Mbps.
This is going to be a huge hinderance to your speeds..
Point number 2. This is single stream AC wireless.. that means it is 433Mbps link speed.
However it is single antenna and that is internal PCB type .. not the external antennas which are only for 2.4ghz.
Add those two things together and you can see why your speeds are so slow.
The Max speed you can get over 100Mbps is around 10MBytes/s and black magic shows you getting a read speed of 5.8MB/s .. remember that is Bytes.. and while a bit slow is not surprising. Due to inefficient handling between ethernet and wireless. If you ran ethernet the whole way it would be hugely faster.
I can stream movies from my TC to my amazon firestick (which is also in the same 5G network) without problems.
At least with both on the 5ghz network you do have a bit more bandwidth. And streaming does not require speeds greater than 100Mbps.
Can you help me?
The AC version TC is hugely superior router to the Asus.. bottom of the barrel model.
It has gigabit ports and full 3 stream 5ghz. I would advise you to put the Asus behind the TC rather than the other way around.. definitely use the TC wireless.. to your iMac and it should give you dramatically better speeds.
Point 3.. SMB has a problem with signing.. You Mac will try to use SMB1 to the TC and there are issues now.. it might work better if you mount the TC disk in the computer using AFP .. ie in Finder.. Go.. Connect to Server.
Type in AFP://10.0.1.1 (whatever the IP address of the TC) when Finder brings up credentials remember to store your password in the keychain.
Then try it.. I think you will do somewhat better with AFP than SMB.
For SMB do turn off signing.
Turn off packet signing for SMB 2 and SMB 3 connections - Apple Support
Not directly relevant since TC does not support SMB2 or later.. but it does seem to affect things.
BTW you should do a test using ethernet only to the TC.. wireless off on the iMac to get a best possible speed. The TC is never that fast.
See Tesserax tests for speed.
AirPort Disk - Throughput Testing
