The digital waveguide mesh (DWM) and related finite difference time domain techniques offer significant promise for room acoustics simulation problems. However high resolution 3-D DWMs of large spaces remain beyond the capabilities of current desktop based computers, due to prohibitively long run-times and large memory requirements. This paper examines how hybrid room impulse response synthesis might be used to better enable virtual environment simulation through the use of otherwise computationally expensive DWM models. This is facilitated through the introduction of the RenderAIR virtual environment simulation system and comparison with both real-world measurements and more established modelling techniques. Results demonstrate good performance against acoustic benchmarks and significant computational savings when a 2-D DWM is used as part of an appropriate hybridization strategy.