First of all I think this is a great forum!

I have read the sticky on suitable subfloors, and along with other reading I am left with few questions/concerns still.

Preface: I would really prefer not to have any underlayment, but my 5/8" OSB subfloor is not suitable for ANY 3/4" solid T&G hardwood installation, right? Is this true even with the "stregth axis" of the OSB being perpendicular to the joists? I read that it is possible to reinforce the joists with 2x6s. Would this suffice? (I believe they are 16 OC)

And I have another question, the joists in the hallway run perpendicular to the rest of the living/dining room. Does this mean I have to install diagonally if I want the wood to all run in one direction?

Any insight would be great. Thanks guys!

On a diagonal would work best with little work. You will need at least ½ plywood over the existing OSB, to run it anyway you wish and not worry about joist direction.

Blocking will not help any unless you were going to install it parallel with the joist. 5/8" OSB does not meet the minimum set by NOFMA and the NWFA. But there are thousands of houses across this country where solid hardwood was installed over it.

The few times I have had an install like this I used 3/8" CDX plywood as an underlayment.

Thanks for the reply guys...
The preferred direction would be parallel with the joists under most of the floor (living dining), although the idea of it laid diagonally intrigues me (if it much harder? I mean do you just blind nail the first row right down the middle?).

But if I do it parallel I definetly need to do some reinforcing... are blocking the joists (how often?) or laying CDX comparable solutions? Because I have some tile next to where I will be laying the hardwood and I feel it will be that much 'lower' than the hardwood portion and it might look funny.

Any comments/suggestions?