Lets back up.. If in fact they are 2 8 uF caps equalling 16 uF in a parallel design, yes you could go to one cap.. however the reason they were probably in there was that whatever that manufacture is they used might have been cheaper to use 2 of the 8's... opposed to a 16.. or simply that manufacture does not even make a 16...
However if you can get a very good 16 uF that is guaranteed better quality than the current one in there so be it and go for it. Or you can go with 8 uF's again due to its more rare to find exotic caps in exact large sizes, for example you might find that mundorf might only make a 12 uF and an 18 uF... So you can't even get the 16 uF unless they offer you to make a pair custom which will normally cost you a lot more... Thats why then you can choose to keep the dual 8 uF's.. which is called "Battery together" type config... or parallel.
Anyway technically you do have a little higher voltage capability with the dual 8 uF's over a single 16 but that has no real application in a speaker accept that some manufactures might argue that the 2 caps are still better with 2 small reserves and faster than one big cap.
Finally the best caps are for the cheap side Jantzen superior...
Mundorfs are in the middle, but I feel in most applications the Jantzens have better bass and just as good for less money..
And on the High side for the better pricing is the Clarity Cap MR's which none of them equal in sound, or you have to go into very costly and much time to get(so have patience) Duelund capacitors.
