Based on my experiences, the communication - that is, the meaning or semantics of the interaction - is instantaneous and telepathic. Telepathy in this state, as Terence Mckenna noted, means "seeing" what another individual is thinking, as opposed to "hearing" it - and this communication often occurs through semantically laden visual imagery.
In addition to simply "grokking" what the entities "mean", I also experience various audible sounds and noises that they produce. These are strange, indescribable, and totally alien sounds, uttered in some inscrutable way - it may be akin to verbally speaking, or it may represent the entities' vibrational/ energetic frequency signature. Different entities seem to be accompanied by different sounds. With DMT, I have never heard anything spoken in English, or any other recognizable language for that matter.
On rare occasions, I have also experienced music in hyperspace. Again, this music is extremely alien and very hard to describe, or even remember well. In one instance, I recall the music sounding bell-like or chime-like, and it being very soothing. Ultimately, the music of hyperspace sounds nothing like I've heard on earth (I'm a musician myself), and I don't think it's structure, intervalic patterns, timbre, etc, could be replicated with the instruments we are familiar with.
How would you guys describe the music you've heard?