Selective transcoding possible?

[simoncn]

It is the control point that needs to hand over to the alternative stream, not the renderer.

1) The renderer tell the control point what formats (MIME types) it can support
2) The server tells the control point what formats it can provide, in order of preference
3) The control point chooses the first format in list 2) that matches one of the formats in list 1) and tells the renderer to play this format

MinimServer is doing 2). If either 1) or 3) are not working correctly, you will not get what you want.

A further complication for your situation is that ALAC has the same MIME type as AAC audio in an MP4 container (audio/mp4). This mean the renderer cannot tell the control point that it supports AAC/MP4 but does not support ALAC.