You have to maintain the trance.
Once you have a stable trance, you have to deepen it to the point of what EA calls The Rapture.
That is step one.
You also have to learn to expand your senses past their normal limits. The “astral senses” aren’t a different set of senses, but a natural expansion of the physical ones we all take for granted. Your mind already perceives the input from non physical sources, but your conscious mind filters them out because they are deemed unnecessary. What needs to be done is to bring them into conscious awareness.
Meditate and focus on the sounds in your body. Then move outward and learn to focus on the sounds in the room. Then move out further and learn to focus on the sounds in the next room. Keep pushing your hearing outward, becoming aware of all the sounds in your home. Then move into becoming aware of the sounds outside. Push even further until you begin to perceive sounds that seem to have no source. When you reach that level, you have expanded into the astral and you can then begin to withdraw your hearing, keeping your focus on these elusive sounds, ignoring all the others. With practice, you will be able to focus your awareness only on the astral sounds within your current environment.
Working with the chakras can be helpful but it is not necessary nor mandatory. What is mandatory is learning to separate the subtle input from the gross physical input, and that requires learning to ficus.
Konstantinos has some excellent exercises for the senses in his book Summoning Spirits. Another book that has some great meditations for learning to expand the senses is Path Notes of An American Ninja Master by Glenn Morris (the author of that book went through the Kundalini using the practice of Qi Gong, which permanently opened up his perceptions).
Something that might be helpful is to program your mind alongside any exercises. Every morning upon awakening, and every evening before sleep, get into Alpha, and repeat affirmations to yourself like “I easily see and hear spirits,” and “my mind easily perceives spirits,” and “My psychic senses are fully open.”