Reduce jitter on live MIDI inputs

I’m attempting to use Cubase (9.5) as a sound module, with VSTs triggered via USB-MIDI from an external sequencer (a Sequentix Cirklon). I’ve found an unacceptable amount of jitter in the triggered sounds, something on the order of 4-5 ms.

The jitter is somewhat proportional to the output buffer size. I’m using a rather large buffer of 256 samples, but even reducing the buffer to 64 samples does not bring the jitter down to acceptable levels.

If I record the same stream of MIDI notes that is being used to trigger the VSTs, there is far less jitter in the recorded notes – well under 1 ms. This is of course without any quantization. So Cubase is apparently “aware” of the correct timing of the notes, but notes that are monitored live do not seem to benefit.

I believe that Cubase is playing the sounds “as quickly as possible” to reduce latency, but in my case I’m not concerned about latency and only care about the amount of jitter.

What I’m hoping for is some kind of “use system timestamps” option for live MIDI inputs. Is this feasible?