There is that solution above some have found workable. For me at the end of the day ingame AA only makes the VR image a blur.
VR SS is the only way to deal with image quality. You can try using higher SS than SteamVR recommended and for me the easiest way is to use the Per App resolution setting it at 150% or 200% if frames are not too slow ingame.
If your app is stable with it, use 200% App SS in SteamVR coupled with PiTool Fixed Foreated Rendering. That lowers the render res on the edges to lighten the load for your GPU whilst giving nice image in the center.