I would suggest playing either HOMM3 or HOMM5 instead of HOMM6, i personally like HOMM5 the most but a lot of people like HOMM3 more, probably because of nostalgia
. Just buy either one of those with all the dlc's and you have much more content than HOMM6.
Other than that there's not really that many games in this genre... If you like complex grand strategy that doesn't have fancy 3D graphics and combat but certainly are one of the best games when it comes to strategy, you should check out Paradox games like Hearts of iron series, Crusader Kings 2 and Europa Universalis 3.
I can't think of any other good TB games like KB series right now, there really isn't that many out there.