Hi Ajahn,
Rocks and chairs are certainly suffering when somebody hits us over the head with them! 
But they aren’t suffering when we’re not aware of them. They aren’t by themselves suffering, as metaphysical “entities”, is what I meant, assuming that they may exist as things independent of awareness, which seems reasonable enough.
Or are you saying that rocks and chairs, or the things they’re made of, exist only when we’re experiencing them? For early Buddhism I’d say that would lean too much towards metaphysical idealism.
When the Buddha defines ‘the world’ as the senses and their experiences, I don’t think he is saying, “this is all there is in the universe” but instead “this is ‘the world’ you should be concerned with”. He’s trying to prevent the whole metaphysical discussion we’re having here! The discourse with Rohitassa you mentioned, to me is a clear indication that the definition is a pragmatic matter and not a metaphysical one. Rohitassa wants to travel to the end of the physical world to find the end of suffering. The Buddha effectively replies, “That won’t work. Look for the end of ‘the world’ of the senses instead.” He isn’t explaining to Rohitassa the idealist view that, “the world exists only when it’s experienced” or “all that exists is experience”. That doesn’t seem to fit the context to me. The Buddha is replying not to a metaphysical question but to Rohitassa’s pragmatic error (one which, moreover, seems exaggerated to make a point). His “definition” of ‘the world’ is of the kind “mother’s milk is blood in the Noble One’s dispensation”: not a literal definition but one that gets us thinking differently.
Idealist ideas aren’t spelled out elsewhere either. There are indications to the contrary, though, that things are assumed to exist even when they’re not experienced. In MN28, for example, Sāriputta gives a situation where the senses exist, the sense external objects (e.g. forms, sounds) come within their range, yet still no consciousness arises. This indicates he assumes things to “exist” even when not experienced, even if it’s clearly not meant as a metaphysical position, but just done out of pragmatism/common sense.
So I think Ven. Vaddha had a good point. All we can know about the world is through the six senses, but from that we can’t conclude that experience/suffering is all there is.
In fact, it seems common sense that there are things outside of experience. All the little pebbles and rocks around my hut are in the exact same place every time I get back there. The easiest explanation for this is that they are simply there in some form even when nobody is aware of them. And at that point those rocks and pebbles aren’t suffering. That’s what I meant.
Again, not that it matters whether things exist outside of awareness or not. My whole point is that this type of metaphysics is irrelevant to the path, to such an extent that the Buddha wouldn’t even engage the whole debate—if it even was a lively discussion at the time, which I highly doubt.
You might be thinking of “life is suffering”. Which actually is very close to, almost literally, a quote of the Buddha. But that’s another subject.