the hub 6 is often referred to SH1
Sh2 cannot split 2.4/5ghz networks but you need sh2 for digital voice
This may help you with regards to your question.
With the BT Smart Hub 2 as already stated, you can not split to 2.4GHz or 5GHz bands
You state this:-
The SH2 supports Complete Wi-Fi, Dect, Digital Voice & G.fast. The SH1 doesn't.
But what in practice does it give me?
What is difference between Wi- fi I get & complete Wi Fi?
What is "Digital Voice"?
Some devices don't like the 2 bands having the same SSID, some people like to be able to force a device to connect to one band or the other.
Complete WiFi are the add on black WiFi discs to give extra coverage. Digital voice is BT's version of VoIP.