The accident occurred just about halfway between Manaus and Brasilia (a 1,200 mile leg) so it would appear that the aircraft were on reciprocal courses, well into cruise and that if either or both of them were climbing or descending it would have been due to weather.
Local news reports said that the Legacy was cleared to fl 330 and the 737 to 360.
The Legacy landed at Cachimbo airforce base which can be seen clearly on Google Earth at 09-20-09 South 54-58-03 West. The accident coordinates provided by a radio amateur last night, based on a farmer's eyewitness account, were 09-47-58 South 53-39-35 West. It is extremely remote but there are small towns and quite a lot of land has been cleared. "Cleared" does not necessarily mean turned into flat farmland, just deforested leaving stumps. The remaining forest, and there's lots of it, is very tall and dense. At the time of the accident there would still have been light.
Re news reports not confirming the collision theory, they are just that, advice that the cause of the accident has not been confirmed as a mid-air.