Question

I and my partner want to divide up a recording studio that we jointly own, which is located in a room in his house. 
Question regarding the appraisal: there are foam panels that were specially fitted to the walls of the room. On the open market they have almost no value, but when they are fitted to the room, for the room’s owner himself, their value is like what they were worth when purchased, or even more. In such a case, do we relate to their value for the partner, or to their general market value, when on the market their value drops very sharply because of lack of fit, etc.? The same question applies to computer software installed on the computer that cannot be removed. For the owners themselves, its value is like the value of the installation, since it is tailored exactly to his needs, etc. But if we try to sell it on the open market, this would increase the value of the computer itself only slightly, if we sell the computer, and no more. So here too, do we go by the value of the item in the eyes of the partner, or by the item’s market value? 
(I seem to recall a similar but different discussion about someone who damages a family photo and the like, which is worth much more to its owners, etc. …)