@markley - start with cables. Once you have them n place it’s easier to discern improvements when changing components and speakers.
A very good brand is Audio Envy - great cables at affordable prices.
Next step up from there would be Zavfino
Here’s my thread as to why cables make such a huge difference
I’ve made cables for around 15 years and had great success on rigs of varying prices, from $350 to $70k
Your system can sound much better with the right cables
Once he cables are in place I would then repalce the speakers - Tannoy make some excellent speakes for an afordable price - but there are so many good brands to choose from
Good Luck with your quest - Steve