Looks like I've been summoned
@ flaviosr
Are you using AMPlifier or AmigaAmp? AMPlifier was developed by the same team that did the Melody card, and supports some other retargetable audio standard called X-Audio. (I suspect it's the only program that uses X-Audio and I also suspect that paulaaudio.device and melodyaudio.device are the only drivers for it).
To get AHI 100% operational, you also need melody.audio and the MELODY audiomodes file (see the readme in the Aminet archive for where to put them).
Also note that AHI 4.18 is fairly old. The current version is 6.x. One of the key differences is that increasing the number of audio channels for each unit in AHI 4 decreases the overall output volume. So if you've set up an AHI unit to have 32 channels, you're probably not going to hear anything. This bug/feature is changed in AHI 6, so you'll have full volume regardless of the number of channels enabled (as long as you set the cycle gadget in AHI prefs to Full Volume).
There are a couple of buggy programs that choke on AHI 6, though. Abuse is one, so if you play that a lot you might want to reconsider going to 6.x. I haven't personally encounted any other problematic programs, so I recommend upgrading.
