The length of your data in words is stored here.
        So, your data must be an even number of bytes, and
        may not exceed 131,070 bytes.  (i.e.  65535 times

However, it is possible to play waveforms longer than 131,070 bytes due to the fact that the Amiga buffers the contents of the AUDxLC and AUDxLEN registers by using backup registers. If you change the AUDxLC and AUDxLEN registers while the Amiga is playing a first word of the sound, then it will start playing new data only after the whole sample has been finished! Any of the Amiga's audio channels can cause a level 4 interrupt just before your sound starts a new waveform cycle. When this interrupt occurs, you know it's safe to change the registers. One warning however: Interrupts caused by high-frequency waveforms can occur quite rapidly. Even more rapidly than the operating system can keep up! It's best to leave the audio interrupts alone, unless you actually need them. Just wait a little while before changing the AUDxLC and AUDxLEN registers and all will work fine.
Interesting links: