Hi Ravyns 

2 excellent Bryce Users named Franontheedge and Dan whiteside told me how to make these file types. To make an obj file or 3ds you have to make sure that every object and every group is not set on neutral set them on either positive or negative. Also What suggest you do is when the model is set ready save in the create folder and then import them back in press the c for convert and make sure the resolution is high for selected 64 is fine 128 is better. then once the object is a mesh go to file/export object and save in a folder for these files(I don't think it matters too much what folder as I use different one for different things.) create a new document and go to file/import object and once you want to make sure its set to object and material. and Bryce should import it if they are objects missing you will need to use the object in the create part of bryce reimport it and then make absolutely sure nothing is set on neutral. 

Hope that helps a bit

Karl 

PS if you use Mac like I do there is a problem with the mac version as I have found if it has over 24,000 polygons it refuses to convert and crashes I am not saying its like it for all macs but it certainly is for me.