The issue with liq is that it has no concept of a "processor", it can decode from a pipe, encode to a pipe, but not easily send to a pipe and get data back. Or at least, so I see it. I've asked about that on their mailing-list. Because of this, I need to use an external encoder, but then must compress directly on the pipe, and thus can not use other encoders afterwards in liq... With jackd, I can output to it, let ST do its magic, and input back in liq from jackd.
btw, there are ways to do better than the provided functions in liq, see this: https://gist.github.com/130db/6001343
but this is obviously offtopic
And this you can leverage ladspa, there are many things you can achieve. But in my experience, nothing as easily tunable & efficient as what ST does.