WinCE versions of BASS and the BASSFLAC/MIDI/OPUS/WV/enc add-ons are available here: www.un4seen.com/stuff/bass24-ce.zip (updated: 3 May '13)
The BASS_AAC/FX add-ons are also available: www.un4seen.com/stuff/bass_aac-ce.zip
(note: the EXE's stack size may need to be raised from the default 65536) www.un4seen.com/files/z/0/bass_fx24-ce.zip
CE 3.0 and above should be supported, but note that this package is for use with ARM CPUs only. Support for other CPUs is also available on request.
Most of the standard BASS examples have been ported and are included, but there are a few still to be done (those that require some work to fit on the screen!). An "mp3-free" BASS.DLL version is also included, which makes use of the MP3 decoder included in Windows Mobile 5/6.
All of the main BASS features should be supported, but there are some differences to note...
As the WinCE APIs exclusively use Unicode strings, some of the BASS structures have been changed accordingly for convenience (see BASS.H). The BASS_CONFIG_NET_AGENT/PROXY settings are also Unicode.
CE devices generally have poor floating-point performance due to the lack of an FPU, so floating-point channels aren't supported (BASS_SAMPLE_FLOAT will result in BASS_ERROR_FORMAT). The BASS_CONFIG_FLOATDSP option is still available, but it will give 8.24 fixed-point data instead (see the DSPTEST example). That goes for BASS_ChannelGetData too, when getting FFT data or using the BASS_DATA_FLOAT flag (see the SPECTRUM example).
As in the Linux version, a config option (BASS_CONFIG_DEV_BUFFER) has been added to set the device buffer size (in milliseconds). That currently defaults to a fairly conservative 200ms, but you could try playing with it (note that must be done before BASS_Init) to see how low you can go without causing breaks in the output.
Support for use with .Net is included in the BASS.Net package.
Please report your findings!