Hey Alberto! Getting the right speaker monitor set-up is essential for hearing everything in your track when it comes to mixing and mastering (and even beatmaking in some aspects, too).
The main problem is that our bedroom studios are typically too small for accurate playback of the low-end bass in our music, even with TONS of thick acoustic treatment.
Without getting too in-depth, the low-end frequencies are the most important to control and tame, which usually costs the most amount of money to treat.
So when it comes to choosing speakers and headphones for music production, usually middle of the road is good enough until you truly learn what's going on with music production.
Once you want to step-up, to get the most benefit, you really want to treat the room properly, and upgrade to a higher-end speaker.
Even for myself at this moment my audio monitor setup and acoustic treatment is okay.. so I end up testing on different audio systems (like ear buds, or in a car) so I can try and get my music to translate half decent before releasing publicly.
For more information, here's two articles that may help further, besides my Music Production Gear Course you mentioned there!
The reference monitor speakers one will mainly talk about making sure to get a big enough speaker. Many people say not to get a big speaker in a small room, but the fact is, if your speaker can't produce the low-end, then you can't hear it! (Right now I'm using an 8" speaker, and that still isn't enough to hear the low-end well.. so that's why I have the subwoofer too.. all middle of the road stuff).
The headphone one will talk to you about open vs. closed headphones, and some other things to think about.
The headphones you mentioned are closed-back, which are ideal for recording or blocking out noise from coming in or leaving the headphones (feedback).. but for mixing/mastering, typically we want to look at open-back headphones.
Please write back with any other points that are confusing you, or where you're at with your music so I can help guide you best in regards to equipment you should look at, what budget you're working with, and what kind of music you're making!
Thanks for your question :)
