I sympathise refsta,
It is frustrating when you outlay the cash and are unable to produce a decent coffee.
Most of us here use fresh roasted coffee to make our espresso. Your local roaster can help there. Where abouts are you? There are a couple of fantastic roasters that can help with your bean.
Most CoffeeSnobs use burr grinders to get the best from their beans once they are roasted.
Checkout the threads through out this forum, there are lots of helpful tips. You may even be tempted to get into roasting your own once you see the only specialist equipment you need is a secondhand pop corn popper.
Once you are getting some good quality beans, roasted fresh, ground less then 3min before you use them, tamped firmly into your hot Portafilter you will notice a huge difference, even on your Breville!
Dont dispair! Help is at hand. Keep experimenting and keep posting here, we will work it out together.