The worst of your not so good are the wires. Quality power cords can make a huge improvement and are worth putting real money into since unlike most other components you can keep and use them through many component upgrades pretty much forever. The gold standard - by which I mean not that its the best but rather its more of a entry level benchmark- is the Synergistic Research Master Coupler. Get one of those, use it to compare everything else against, and you will be fine on power cords.
This will do a lot to help the problem of things getting lost in the mix, a lot of which is due to loss of signal detail. Everything contributes to loss of signal detail. So its not like there's one thing you can do. Its a lot of things. They all add up.
In terms of components the one that will make the biggest impact in bringing all those sounds from buried to life and make your music sound live is new speakers from Tekton. Double Impacts are in your budget and will transform your system in exactly the ways you want. If you have the room and the budget then order Moabs like I did, you will not be disappointed.
Now for the MIA: SR HFT, ECT, PHT, Orange Fuse, Cable Elevators. Each of these will do exactly what you want, improve clarity and bring those lost in the mix sounds out in the open where they belong.
None of these will change tone or balance. When you talk about some instruments being lost or too prominent that is usually a tone or frequency imbalance of some kind. Usually speakers (and Tekton will fix that) but could just as easily be your wires or amp. Freebie rubber power cords are pure crap but at least are balanced in their crappiness across the board. Aftermarket wire on the other hand, while it can be hugely better it can also often times be the betterness comes at a cost of crapiness in certain areas. That is why I recommend SR as being the most uniformly and reliably across the board better. Not necessarily the best at everything, but almost always the best overall.
HFT, ECT and PHT will greatly improve clarity, imaging, and make your speakers disappear. HFT and ECT are all very uniform and neutral. PHT come in different flavors. I've tried them all and Green Dream is super luxurious and deeply sexy, while Black Beauty is a little more neutral and dynamic. I recommend using both together and the people who have taken that advice tell me they are very happy indeed.
SR Blue and Orange Fuse are around $150 and roughly equivalent to a $400 Master Coupler so the Fuses are a no-brainer. But really there is no right or wrong way to go about it. There's also vibration control, BDR Cones, a Shelf or sand box for your turntable. Every one of these ideas will be a step in the right direction. It all depends on how far you want to go.
https://systems.audiogon.com/systems/8367