Let's start at the beginning. Why did you buy the WiiM Pro Plus in the first place? It's main use is that of a streamer that happens to have a good quality DAC (in case you don't already own an even better one) and extended sound controls, including(as of recently ) room correction. The latter works irrespective of if you are using the analog output (using the WiiM's DAC) or one of the digital outputs (using the receiving devices DAC).
A DAC is not inserted into an audio chain to improve anything. Digital audio signals must be converted to analog before a speaker can reproduce the sound. DAC and DSP are totally different things, as
@Wiimer already pointed out.
The TCL Alto 8I is a rather low price soundbar featuring its own DAC. With respect to the price its in-built DAC is probably inferior to that of the WiiM Pro Plus, but it's questionable if there's a difference to be heard.
If you just want to listen to TV sound through your TCP Alto 8I there's probably no point in adding any device in between.
If on the other hand you want to listen to music from streaming service or a NAS in your network, the the WiiM is probably superior to your TV. If you want to use dime grained EQ to tailor the sound to your needs, then the Pro Plus is a good choice. You can pick any combination of input and output settings, as long as you have a matching device connected to each input and output.
The limiting factor regardingbsound quality will be this soundbar.