I'm right in 'the zone' listening to the ESCO modded Zu 103 cart on my tt thru the Def4s. It so outperforms the 4x more expensive, and more celebrated, Transfiguration Orpheus, that it's beyond a joke.
An amazing synergy is going on between these two components, maybe no surprise since Sean and the Zu team voiced the 4s specifically around the strengths of the Zu 103.
It's no coincidence that the most difficult components to get right in an analogue based audio system are the transducers (ie cart and spkrs). They hold the key to the 'flavour' of the system, and it's so easy to get their choice wrong. Thus it's great that both these components have a deliberate similarity in tone and feel.
So any tt users who are running the 4s, do yourself a favour and get the Zu 103, and even better still get the ESCO modification, you won't be sorry.