Second AP no connection

I am not an expert but saw your msg and want to give a quick reply if you are in Local management mode (I don't use Insight but maybe you could find similar there).  It is around page 200 of the manual.  Under Management-Wireless-Advanced look for Load Balancing tab near the top.  Click Enable and then remove the checkmarks from the first two sections (number of clients and channel load).  Under the third section either leave the slider at default (23) or move it to your desired setting.  This is a number with scale 1-50, lower strength is lower value, so clients with strength below 23 would be rejected.  There is also a Sticky Client setting which has to do with moving already connected clients.

I hope that is helpful, I cannot promise how it works but I wanted to point it out (and mention to disable the checkbox for the other two sections if you want it based on signal strength).  Of course you would try that setting on the 610 since it is the one you say clients are connecting to.