Forgive me if I answer in English, but I'm sure that Google Translator will not be able to translate correctely from Italian to Spanish...
I saw that post, but I'm referring to one of those mini sized DSPs as a first step to the upgrade of the original sound system.
They could be easily mounted on top of the Head Unit, or in any other place under the dashboard, and, as far as I read around, they could give life, literally, to the stock speakers.
Without being too much expensive...
The people have to decide how much money or how much quality they wants. After that, they can choose many options.
I think, the best option is a DSP Amplifier, 2 woofers + 2 twitters and, if you need it (kind of music), 1 subwoofer. If you install only the DSP with the original radio, without amplifier, you will have the same poor power for the channels. The power for each channel (original radio) is not enought for a good quality car audio system.
But I think, the people must to choose the option (Quality and money to spend)