We are certainly going to give you the run around on here! First, please understand that making espresso is, in many ways, like baking bread. You can buy lotsa fancy equipment but in the end you still need skill and knowledge that comes from study and experience. It is also true that baking bread and making espresso are similar in that there is more than one way to go about some things and that that taste is individual and what is "good" or "sweet" or "bitter" means can be confusing to ascertain and communicate.
About the link about tasting and diagnosing. You asked what part to read. It has been a long time since I have read it but I would say you need to study it all. Then in a few weeks after you think you have a handle on things, read it again. I should stop typing this and re-read it now!
Making espresso consists of working with a bunch of variables. Taste in the cup can seldom be contributed to one thing. For example, in your case, the bitterness you want to escape may be attributed to the roast of the bean, the fineness of the grind, the duration of the extraction and the temperature of the water. I do not know which one it is, and really, in your specific case, neither does anyone else on here!
What we do know is that you have these variables to mess with in order to find different flavors that the beans will give up in the extraction. This is what that linked article is trying to explain. Don't toss those beans. Learn from them. Start with say a 18 gram dose and 200 degree temp. adjust the grind so that you are pulling 36 grams of espresso in 25 seconds. It may be sour or you may like it. Begin making the grind finer one small move at a time. Keep the dose, temp and output (36 grams) the same and you should get the 36 grams in like 27 seconds. Taste it. Then move the grinder one click finer. Keep everything else the same. Keep making small changes in grind wile keeping everything else fixed until you are running your shots for like 36-40 seconds. Take notes. When you are done, return to the settings that you liked the best.
This place will likely be a compromise. It will be the best you can find by altering grind. Next, mess with water temperature and dose. Keeping grind, dose and output locked. If you think it is a touch sour, increase water temp. If it is a touch too bitter, decrease water temp. Do each a little at a time. My suggestion is to handle things this way. Then after all this I'd mess with dose, but I would not suggest it now. Other may have different methods, they are probably correct too, but these are my suggestions.
When you are new to this, it can take a lot of coffee to get a bean "dialed-in." for some it is frustrating and expensive. Tweaking these variables are ways you can effect the taste of the extraction. Finally, it is worth it to note that there are some flavors that you may not ever be able to get away from due to the roast or origin of the coffee you are using. Good luck.
As for your Super Crema. Do not despair. Many believe that these Italian blends are made to sit on the shelf for longer than our typical rules of thumb. Read this for suggestions on how to start to pull it. I bought the Kimbo that everyone was talking about on this thread. If I had not seen Dominico's recommendations in this thread on how to pull it, I would not have liked it. Since the Kimbo is an Italian blend, and so is the Lavazza, there is a chance they are develloped to be pulled in a similar style. I have never used Super Crema but if I did, I would start by pulling it the way Dom, recommends for Kimbo and make changes from there. Italian Coffees. Lets talk about Kimbo, Danesi, Lavazza, Caffe motta, Illy