ZamAudio.com has provided several drivers for the ALSA support for Digidesign hardware:
ZamAudio.com - Digidesign Mbox 2: Linux driver provided!
ZamAudio.com - Digidesign Mbox 2 Mini on Linux
ZamAudio.com - Digidesign Mbox 2 – Now part of ALSA!
ZamAudio.com - Digidesign (original Mbox) Linux Driver

Tested to work on Slackware64 14.2 (with latest patches as of 2019-05-04 running self-compiled kernel 5.0.11).

This assumes the steps described on SlackDocs - howtos » multimedia » pulseaudio_non-default were followed to disable and *not* remove PulseAudio.

The following ~/.asoundrc content works to enable a Digidesign MBOX 2 Mini as the primary audio device with stereo (2-channel) audio. The MBOX 2 Mini only suppports the S24_3BE format and as dmix (as of 2019-05-04) does not support S24_3BE dmix cannot be used so only ONE applications can play sound on the MBOX 2 Mini. A patch to add S24_3BE to dmix was provided in 2014 but rejected.

# https://unix.stackexchange.com/questions/74558/change-sampling-rate-in-alsa

pcm.!default{
    type plug
    slave.pcm "device"
}

pcm.device{
        format S24_3BE
        rate 48000
        type hw
        card M2
        device 0
}

Based on an example taken from the Stack Exchange - Unix & Linux - Change sampling rate in ALSA.

Taken from Slackware64 14.2 (with latest patches as of 2019-05-04 running self-compiled kernel 5.0.11).

Command:

arecord --dump-hw-params -D hw:M2,0

Output:

Recording WAVE 'stdin' : Unsigned 8 bit, Rate 8000 Hz, Mono
HW Params of device "hw:M2,0":
--------------------
ACCESS:  MMAP_INTERLEAVED RW_INTERLEAVED
FORMAT:  S24_3BE
SUBFORMAT:  STD
SAMPLE_BITS: 24
FRAME_BITS: 48
CHANNELS: 2
RATE: 48000
PERIOD_TIME: [1000 1820438)
PERIOD_SIZE: [48 87381]
PERIOD_BYTES: [288 524286]
PERIODS: [2 1024]
BUFFER_TIME: [2000 3640875]
BUFFER_SIZE: [96 174762]
BUFFER_BYTES: [576 1048572]
TICK_TIME: ALL
--------------------
arecord: set_params:1297: Sample format non available
Available formats:
- S24_3BE