Howdy, me again 
Considering my current kit - Polk PSW10 10" active sub, and Polk XT15's paired up with the WiiM Amp
If there's anything to consider as a upgrade, where and what would that be - I'm leaning towards the Polk XT15's being replaced first, but maybe the Sub? I don't think the Amp will need replacing anytime soon.
The reason I'm thinking about a slight speaker replacement/swap. My wife would like a WiiM in the entertainment area with bookshelf speakers as well, for casual listening when she's busy in the general area.
Thought about getting a slight bump in quality speakers to replace my Polk XT15's, and give that to her. But what's a feasible upgrade, considering the Polk's size. Looking around and watching reviews, the next tier seems to be around 250-400$, but you lovely smart people would probably know a bit more if it's a better return on investment to replace the sub or speakers first.

Considering my current kit - Polk PSW10 10" active sub, and Polk XT15's paired up with the WiiM Amp
If there's anything to consider as a upgrade, where and what would that be - I'm leaning towards the Polk XT15's being replaced first, but maybe the Sub? I don't think the Amp will need replacing anytime soon.
The reason I'm thinking about a slight speaker replacement/swap. My wife would like a WiiM in the entertainment area with bookshelf speakers as well, for casual listening when she's busy in the general area.
Thought about getting a slight bump in quality speakers to replace my Polk XT15's, and give that to her. But what's a feasible upgrade, considering the Polk's size. Looking around and watching reviews, the next tier seems to be around 250-400$, but you lovely smart people would probably know a bit more if it's a better return on investment to replace the sub or speakers first.