there are many things no one knows about your own military. also i doubt pakistan would have leased a nuclear sub yet. india is in the process of leasing the akula class sub which could be either the kasholot which is undergoing modernisation or the iris which is partly complete it could be either one sub or it could be the two. if so pakistan would lease the type 93 sub from china [type 91 undergoing decommissioning]
when Pakistan decided to purchase 8 subs i would think the sub marines are not the s20 as they are quiet small to accommodate the babur missile. so it would either be the type 32 [which is big] or type 41 possibly enlarged. the first 6 would be conventional and the last two would be nuclear powered and armed that's the best option.
6 aip subs is a the standard quantity as it allows a navy to to use the subs on two tasks. so imagine is as 6 subs, but in two groups of 3. one would be on patrol or undergoing its task/mission. the second would be for training or possibly coastal patrols and the third would be for maintenance or training or reserve/backup.
nuclear sub don't need a lot of maintenance so two subs would be ideal and the less number of subs the lees likely someone sees the subs [foreign intelligence agencies] also it may get its hands on the type 93 to counter the akula class subs being leased
i feel pakistan is more of a thinker and carefully makes it next move. like some playing chess.