any of the Mastering presets on your master bus would give you short term and average LUFS values, as well as the peaks on the outputs. Perceived loudness also depends on the material but if you get the average LUFS values about the same, you should be good.
your best alternative should be ASIO drivers, WASAPI is slow IIRC. If you have Focusrite hardware, there *should* be fast ASIO drivers available for it. Please check the Focusrite site for up-to-date ASIO drivers.
