The Si Expression 1 features 16 recallable mic pre amps plus 4 line inputs, 4 internal stereo FX returns, AES in, and a 64x64 expansion slot offering more than enough scope to use every one of the 66 input processing channels. Every input processing channel has dedicated processing for high pass filter, input delay, gate, compressor and four band EQ.

The 14 aux/group mixes can be configured as 14 mono mixes, 8 mono plus 6 stereo mixes or almost anything in between, whilst the 4 matrix mixes can be mono or stereo as needed. The bus and matrix mixes are complemented with four more mix busses dedicated to the internal Lexicon FX processors all in addition to the left, right and centre busses. Each bus mix features a compressor, 4 band EQ, BSS graphic EQ and delay always available all of the time. Output connectivity is comprehensive with 16 balanced line outputs, headphone monitor out, AES out and of course the 64x64 option slot.