Just been talking to sales abut this product: http://www.theheadphonecompany.co.uk/headphones/unique-melody-unique-melody-westone-3-reshell-quad-driver-upgrade.php
There's no way to check what the extra driver will do for my sound except that it is another "low" driver. Given that bass is an important factor in my music genre my concern is there will be a reduction of bass (even perception of drop). My source is the iphone 5 which has a flat sound eq and as I mostly listen to podcasts there is no way of changing the EQ.
Of course i could just not bother with the extra driver and just reshell with existing drivers only.
The chap i spoke to on the phone had the frequency response graphs but wasnt prepared to let me have a copy. To be honest, I doubt it'd make any difference if I had them or not, the only way I'm going to know is by listening. He did say that the Westone 4 and the Westone 3+1(driver) did not look the same at all. He thought that perhaps UM would try and match the same response by adding the driver.