Actually to say that none of the sliders work is incorrect; only the Oscillator AD, Filter ASDR and Amp ASDR sliders don’t work.
This is the full list of controls the GAIA sends, with the CC# number between parentheses:
BANK_SELECT(0), MODULATION(1), PORTAMENTO_TIME(5), VOLUME(7), PANPOT(10), EXPRESSION(11),
BANK_SELECT_LSB(32), HOLD_1(64), BEND_MODE(90),
// effect controls
REVERB_CONTROL_1(12), DELAY_CONTROL_1(13), FLANGER_CONTROL_1(14), DISTORTION_CONTROL_1(15),
REVERB_LEVEL(91), DELAY_LEVEL(92), FLANGER_LEVEL(93), DISTORTION_LEVEL(94),
// tone controls
TONE_1_LFO_RATE(16), TONE_2_LFO_RATE(17), TONE_3_LFO_RATE(18),
TONE_1_LFO_FADE_TIME(19), TONE_2_LFO_FADE_TIME(20), TONE_3_LFO_FADE_TIME(21),
TONE_1_LFO_PITCH_DEPTH(22), TONE_2_LFO_PITCH_DEPTH(23), TONE_3_LFO_PITCH_DEPTH(24),
TONE_1_LFO_FILTER_DEPTH(25), TONE_2_LFO_FILTER_DEPTH(26), TONE_3_LFO_FILTER_DEPTH(27),
TONE_1_LFO_AMP_DEPTH(28), TONE_2_LFO_AMP_DEPTH(29), TONE_3_LFO_AMP_DEPTH(30),
TONE_1_OSC_PITCH(70), TONE_2_OSC_PITCH(71), TONE_3_OSC_PITCH(72),
TONE_1_OSC_DETUNE(73), TONE_2_OSC_DETUNE(74), TONE_3_OSC_DETUNE(75),
TONE_1_OSC_PULSE_WIDTH_MODULATION(76), TONE_2_OSC_PULSE_WIDTH_MODULATION(77), TONE_3_OSC_PULSE_WIDTH_MODULATION(78),
TONE_1_OSC_PULSE_WIDTH(79), TONE_2_OSC_PULSE_WIDTH(80), TONE_3_OSC_PULSE_WIDTH(81),
TONE_1_OSC_ENV_DEPTH(85), TONE_2_OSC_ENV_DEPTH(86), TONE_3_OSC_ENV_DEPTH(87),
TONE_1_FILTER_CUTOFF(102), TONE_2_FILTER_CUTOFF(103), TONE_3_FILTER_CUTOFF(104),
TONE_1_FILTER_RESONANCE(105), TONE_2_FILTER_RESONANCE(106), TONE_3_FILTER_RESONANCE(107),
TONE_1_FILTER_ENV_DEPTH(108), TONE_2_FILTER_ENV_DEPTH(109), TONE_3_FILTER_ENV_DEPTH(110),
TONE_1_FILTER_KEY_FOLLOW(111), TONE_2_FILTER_KEY_FOLLOW(112), TONE_3_FILTER_KEY_FOLLOW(113),
TONE_1_AMP_LEVEL(114), TONE_2_AMP_LEVEL(115), TONE_3_AMP_LEVEL(116),
(Although I think PANPOT may be in that list by error; I was not able to reproduce it recently.)
Note that it actually sends different controller messages depending on the tone and effect selection. If multiple tones are selected it will send two or three CC# messages for every knob change. So this may expand its use as a controller for you.
To get the ASDR sliders to work, using the
MIDI Solutions Event Processor is a possible solution, because the GAIA does send sysex DT1 messages when they change (if the Tx Edit Data setting is on). Although there is not much CC numbers left to assign them to.