What your drawing represents I believe is a Schmitt Trigger front end using discreet components. As drawn with the values you are using the output of transistor Q3 will swing positive when the input signal threshold crosses right around ~2.64 Volts. You mention needing 4 channels.
In keeping it simple for 4 channels why not use a simple LM339 quad comparator? Your input signal would go to a positive input and the negative input would go to Vreference (2.64 volts) and a simple 10 turn pot could be used to adjust and set your Vreference. It seems all you are concerned with is triggering at some preset input level. If I read this correctly a LM339 quad comparator could manage all 4 channels on a single small chip with a small handful of resistors. I wouldn't get to hung up with the TTL level to CMOS level thing. I can make a cartoon if it would help but what I am thinking **broken link removed**
Ron