I am not sure what your preference to stones may be, or what type of budget your working with, but if your only going to be doing two knives I am comfortable saying that which ever stone(s) you choose should last a long while including a combo stone.I still question if my initial choice of a king 1k 6k combo would have been a better choice then the multiple singles I have purchased, and it would have saved some $$ etc. I guess if you intend on getting more into sharpening then the thicker more expensive single grit stones make sense as you will be adding to your collection etc, but if your just looking to keep a good edge and have no intent on sharpening several knives often, and are not looking to work your way up to a 10K down the road the combo will save you some $$ up front, and may be all you need.
Also though everyone is different and so are sharpening skill levels etc I am not sure if I would like my Tojiro DP knives as much if I stopped at 1K, Actually the least I have done on those is 2K and though it is :"well enough" etc the VG10 core will take a bit more polish and I find I am happier when I have time to take them to 6K.
A lot depends on what you want to do, and what you like etc, and most recommend a 1K as the best first stone for various reasons, and you can get a shaving sharp edge from a 1k too, but everyone is different and I actually just got my first 1K this year, and pretty much use it only when i need to remove a good amount of steel like you would do when removing a small chip or thinning etc ( I know a 600 or 800 might have been a better choice in retrospect, but at the time 1K seemed fine lol).
Lastly since I have both of your original choices in different lengths etc I am confident you should be happy with either the FKM or DP, and though they are different they share a great price point perform well too!