First of all much thanks to everyone that has helped me with my project. The frame went up very well, I'll have pictures later, but for my immediate concern.

For my 2nd floor I've chosen 3/4" T&G pine (1st floor ceiling), then a layer of 1/2" "Homasote 440", and finally, a layer of 3/4" fir plywood for a subfloor. I'm screwing down the plywood with 4" screws into the timbers below. For equal spacing, my floor joist are 32" O.C. My concern is, that I don't have enough fasteners close enough together and the floor may feel a little spongy between joists. 32" is quite a gap between screws, typically it would be 16" O.C. in conventional framing.

My question...... can I screw the top layer of sub-floor to the pine boards below, carefully with the correct length screw. Obviously I'm proposing screwing between the floor joists. The correct length screw would be 1-3/4" or 1-5/8" slightly countersunk. I'm worried that as the house ages and such, the boards may split where I've screwed to them, even though the screws wouldn't be poking through. What do you all think???

I think you'll find the floor is plenty stiff without the interim screws. I'm using a single layer of 2x8 T&G Southern Yellow Pine on 30" centers, feels solid as a rock.
I'd put it together with just the screws into the joists at first and see how it feels. Another option would be use construction adhesive to bond the Homasote layer to the plywood.

Thanks. After putting the floor down I was wishing that I used a 2x6 or 2x8 T&G, then possibly homasote and plywood.

The reason for all the layers is...... I'm cutting out wiring chases in the homasote, then covering them with plywood. I'll just need to be very careful not to nail through the wires when putting down the finished floor. I'm considering putting down some type of metal over the wires to protect them.

Does anyone else out there have an opinion or word of advice?

I did the same thing on my frame. I used 1x10
pine boards, a layer of osb, and then 1x10 t&g
heart pine. I screwed and glued the osb to the
pine ceiling and haven't noticed any cracks.

Your built up floor is not going to stiffen much for having been layered for the same reason that you can bend three 1/4" rips easier than you can one 3/4" board. The layers will move independently esp. with that homosote and mechanical fastening. If you can adhere the homosote both sides with an adhesive it might stiffen but I wouldn't count on it. You could consider going to 1" or even 1 1/4" plywood (makes my back sore to think of it)
As for the wire I have used Simpson framing strap over wires but I don't know that that would be code approved
If there is not much wire you might think about 1/2" ridged conduit.

I think John is right that you are going to need 1" or 1-1/4" plyweed to have a stiff floor. Your lumber salesman should be able to get you some stuff rated for 32".

cheers,

Gabel