AVFAN comment.
I suspect due to cable Cat5e

tx6 comes in several configurations, specs can be quite diff but all are 100mbps ethernet.
some 2+16gb, some 3+32, 4+32..., some 2.4ghz only, some 2.4/5ghz.
u should take a good look at the specs of what u bought.

from your results, i think yours is one with 100mbps ethernet and 2.4ghz wifi only.
100mbps means max capability of the rj45 port of the box is 100mbps... getting 70-90 is a tad low; it depends on router and what app u use to test.
u can change to another cat5e or cat6 LAN cable, may get 103-108; possible the cable u have is a poor one.
wifi 2.4ghz should be able to do >100mbps; then again, cheap boxes having poor wifi modules are quite common.

tx3mini/max is like tx6 for ethernet and wifi - 100mbps, 2.4ghz only.
in contrast, a tx5max has better specs, rj45 port is gigabit.
i get 830mbps with ethernet and >200mbps wifi despite my router being a mediocre one.

300mbps available... what wifi speed u get on any device even with 5ghz depends on your router and the device itself.
stock and cheap routers, u might not even get 100mbps; better ones get 150-250; those that can get >300 will cost u rm2-3K.
assuming the device is capable as well.

this subject has been trashed to death:
https://forum.lowyat.net/topic/4658454/+180
https://forum.lowyat.net/topic/4658096/+1220

lastly, live hd tv streams do not require high speeds.
netlfix hd/4k requires 25mbps only... in reality it only uses 8-12mbps.
astrogo hd works fine with just 10mbps stable speed.
other hd streams - about the same.

it is when the speed is unstable that u can't stream properly.
this is likely your problem.
u should use ethernet for better stability; and consider buying your own better router for better wifi.