Henning, I don't own either speaker, but I frequent a dealer who carries Linn and seeing as I want to get the ESPEK down the road, I've listened to both numerous times.
The only thing different between the two speakers are the drivers. They are updated in the ESPEK (from what the dealer told me). In fact, if you have the 5140, you can turn it into the ESPEK with a simple upgrade of the drivers from Linn. The cabinetry is the same, the crossovers are the same I believe. Not sure about any other subtle differences, but I believe the ESPEK sounds better but that's from memory, and I couldn't tell you exactly what I preferred in it over the 5140 because it's been a while since I heard the 5140. I never had a chance to hear the two side by side.