Great - now we are getting there...
We now know you have a keyboard controller - somyou simply need to hook this up directly to your computer with a USB cable
This one for £3.99 will do the trick:
https://www.amazon.co.uk/AmazonBasics-USB-2-0-Cable-Male/dp/B00NH11KIK/ref=sr_1_3?ie=UTF8&qid=1528486417&sr=8-3&keywords=USB+b+cable The keyboard does not need to connect to your audio box at all
The audio box connects to another USB socket on your pc (or if you run out of USB sockets you can get a cheap hub - in theory it is best to connect your audio interface directly to the pc but I run mine off of a hub and it is fine)
I don't think the 32 v 64 bit will help much with this bit
The buffer size is the key bit - which is what Presonus are calling "block size"
These settings work for everything I've tried except the most musically complex synths running 4 to 9 instruments. So to use those, would I just lower the block size again until it works? I can live with that
No - you would need to INCREASE the block size as your system starts to struggle
The lower the number the less latency (the time between pressing a note and hearing a sound) - but the lower the number the more strain you put on the pc processor so you can get crackles, pops, (static) drop outs and even the system not playing audio as you place more strain on it (i.e. By opening lots of soft synths
If you raise the buffer size you take the strain off of the pc so it should play better BUT you will increase the latency and start hearing a delay between pressing a key on the keyboard and hearing a sound
You therefore need to find a balance that suits you where your system plays without "static" but you don't hear so much of a delay that you can play along
A good trick to use if your system is struggling is to RECORD with minimal effects and plugins and have a low buffer/block setting (256 or 512 may be low enough)
When you have recorded everything you can raise the buffer level (e.g. 1024 or higher) and start adding different softsynths (e.g. Swap some out for more resource hungry versions) and your system will cope better
Even more modern systems could struggle with 9 complex soft synths and a really low buffer setting