Even though this thread is a bit older, there is a plausible explanation why TL-Audio removed the SSM2017 and used a well-known and proven input circuit instead. 1. In the SSM2017 circuit, the LineIn was fed to the "microphone input" via a simple voltage divider (40db 100 times). This is not particularly subtle, as the microphone preamplifier is only limited to 20 kHz for HF safety reasons, while the frequency response otherwise goes up to 40 kHz.
2. The SSM2017 and its successor, the SSM2019, had relatively high failure rates, particularly with long cable lengths, high capacitances built up, which "destroyed" the very sensitive SSM despite limiter diodes... The NE5532 circuit with the 4 input transistors was very robust in comparison...
3. In the new circuit, the Line IN input with 2x NE5532 has a completely separate path, but is sent back to the "microphone main path" before the impact sound filter and Pgase Reserve. Now with reasonable impedance - without voltage divider and cutoff frequency 40kHz. That is serious and much more professional than the SSM 2017 circuit. However, since the company had previously done a big advertising campaign regarding the TOP quality feature of the SSM2017 - but a rather unprofessional Line IN 1:100 attenuation - they had probably quietly corrected this error... Well - unfortunately, the company closed in 2012. Nevertheless, the VTC console is a dream in terms of sound for me personally... I have the 24-channel version and am really happy with it... The first circuit with the SSM2017 came out in 1999 - the revision with the NE5532 in 2003. My console is probably from 2006. There are also strange versions of the power supply. The circuit diagram shows 56,000uF unregulated electrolytic capacitors behind the rectifiers. But in my case it is only 22,000uF in the power supply. I will definitely modify that. My console has a signal-to-noise ratio of around -84 dB with 24 connected channels... That's a great value, slightly overlaid with a residual hum - which could be due to the not low values of the electrolytic capacitors.