Soo you have 2 options;
Option 1:
I7-4790 recommended price from 175$-250$
GA-H97M-D3H 70-80$
You have ram Is it single 8GB stick or 2 sticks of 4GB? (Download CPU-Z and post screenshot of SPD tab) It would be good to buy atleast to 16GB
Here's<- product page
As for GPU you can go for used 980 and basicly max out any game at 1080P and stream without an issue same as 1060 6GB (MRSP or stock/release price should be 200$ try to keep close to that price) (try to buy it in local shop) any brand will work.
As for price of the GTX 980 it should be around 250$.
And I advise for buying an new PSU like SeaSonic G series 550RM, Corsair CX500M, seasonic s2ii 520w.
Other possible option is to sell that current rig with ram and buy new ram.
Here's link for motherboards page;
"here"
Second option;
Well buying everything new.
PCPartPicker part list /
Price breakdown by merchant
CPU: Intel - Core i5-8400 2.8GHz 6-Core Processor ($178.89 @ OutletPC)
Motherboard: MSI - Z370 SLI PLUS ATX LGA1151 Motherboard ($112.90 @ OutletPC)
Memory: G.Skill - Flare X 16GB (2 x 8GB) DDR4-2400 Memory ($157.99 @ Newegg Business)
Video Card: Asus - GeForce GTX 1060 6GB 6GB Dual Video Card ($289.98 @ Newegg)
Total: $739.76
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-05-15 13:42 EDT-0400
Same goes for PSU and for GPU's.
Just to add, Amd side is RX580/480/470/570,
Note; Option 1; build are mostly used parts except PSU and 1060 6GB if you are willing to buy it new, if you are willing to sell current rig then I advise you to look up to the memory compability from motherboards site
"here"
Note2: i Know that I went overbudget with i5-8400 but with 8GB of ram its tight to stream, since you're gonna hit ram limit, thats just how it should look if you are going for new parts.