Real Time Control
The Holiest Grail can send and receive MIDI continuous controller 
messages, allowing external sequencers to record and automate 
parameters. 
The Holiest Grail sends and receives MIDI CC over Channel 1 only.

Each slider (except Input Level) has an associated MIDI CC code:

CC#
20  Pre-Delay Time
21  Pre-Delay Feedback
22  Reverb Decay
23  Reverb Damping
24  Reverb Diffusion
25  Dry Output Level
26  Spring Output Level
27  Reverb Output Level
28  Bank Selector (CC is not saved and does not affect program load)
30  Footpedal/CV Input

Each time you load a Preset, all of the slider values for that preset 
will be sent out as MIDI CC messages. So you will receive 10 MIDI CC 
messages every time a preset is loaded.

MIDI Program/Patch Change
The Holiest Grail accepts MIDI Program Change messages to load any of 
the 8 presets.
The Holiest Grail receives MIDI Program Change on Channel 1 only. 
Sending any of the following MIDI Messages to the Holiest Grail will 
load the corresponding Preset:

MIDI PGM 0 Bank 1, Preset A
MIDI PGM 1 Bank 1, Preset B
MIDI PGM 2 Bank 2, Preset A
MIDI PGM 3 Bank 2, Preset B
MIDI PGM 4 Bank 3, Preset A
MIDI PGM 5 Bank 3, Preset B
MIDI PGM 6 Bank 4, Preset A
MIDI PGM 7 Bank 4, Preset B