Where’s My Weakest Link?

You mention your cables are "generic" like Amazon Basics generic, or some such? Cables can make ALL the difference. You don't have to spend thousands (though you could). A good start is power. Like MC said, do your outlets, easy and relatively cheap. Then power cables. Lot's of options. Look within your budget, check the a-gon ads etc. Then look at your speaker cables, same thing. Last interconnects. See what you wind up with. Keep in mind cables are a slippery slope. Once you have a set of cables that work well, then think about maybe upgrading components. Then, if you want from there, tweaks. And yes, the room can absolutely be everything. Very important. 

@almarg has presented some very relevant facts. The OP has aging components that should be addressed first. Plus, I doubt that his amp and preamp are revealing enough to warrant adding tweaks such as aftermarket outlets and power. 
Building the foundation of the system should come first. As stated earlier, an integrated amp would be a good way to go.

Don’t replace the Node 2i, it is very nice little streamer that would cost three times its cost to exceed. If anything, in the future you might consider adding a stand alone DAC, but again, multiples of its cost for any real benefit.

There are other things to consider first.  After any basic (and needed) hardware changes, I would buy Canare 4s11 speaker cables and Canare L-4E6S interconnects from a vendor such as Markertek or Redco.  The total for the above very nice cables would be very reasonable cost.

Between your ears. Seriously! Put yourself in a better mood and your system will sound better. Otherwise, get two subwoofers and a 2 way crossover.

You simply aren't using the right fuse - it's the only thing holding your system back from it's full potential.

Honestly, pound for pound putting effort into room acoustic treatment will likely make the biggest difference. I wouldn't start making gear changes before getting the room right first.