Probably not much help but I have heard both the predecessors but in unfamiliar surroundings. Both good amplifiers I'm sure with equal power.
The Exposure is more hair shirt but you do at least get a r/c.
The Arcam has a headphone amplifier, MM phono stage and I believe you can adjust input sensitivity and re/name inputs. It would be my choice of the two.
unfortunately both is at the moment not possible. No dealer around me has the new Arcam A39 and from Exposure there will be next week the new verion of the 3010S2. Don't know what are the difference but the distributor told it sounds more open. I can become the new verion og the 3010S2 for the old price of 1400 Euro. The new Arcam will cost 1620 Euro.
I've heard the old Exposure 3010S2. It sounds very good, but maybe for me too much forward sounding and too lively. With my music, metal and rock, i lke a less "busy" presentation.