remote extender for harmony one

Is there any reason why a remote extender will not work with the above universal remote. It will be used for amp,blue ray(eventually) and hd/dvd recorder. These are in a cupboard at present. I previously used a nifty device from keene electronics which was a rf transmitter to replace the battery in any remote. I then used this in the amp remote to control amp and dvd player. Unfortunately ,for some reason, this only intermittently controls the volume on the amp. I am now thinking of a universal remote due to having  a new pioneer 5090 with no speakers and everything going through the amp(this is confusing the rest of the family).

 Can anyone suggest a remote extender which is fairly inconspicuous as most seem to be quite large, therefore reducing the benefit.

 On a different note isn't it time manufacturers started addressing the issue of  the increasingly common practice of having dvd players etc in cupboards by providing some easier solutions. My portable incar dvd player has a ir detector on a wire which must be easy to do.Also my pioneer all in one from 10 years ago has a seperate display and ir detector which is remote from the player itself.

 Thanks for any help . Hope I was clear enough and haven't wittered too much!