Question Sampling from diffuse (and other) GBuffers for deferred HDRP post processes

Hi, I'd like to ask for help here. I'm implementing an SSGI post process, with HDRP in deferred. I have finally everything working (at least it seems like it). But when applying the final result of the sampled global illumination (/indirect lighting) from the nearby environment, I need one last piece of the puzzle - to be able to get diffuse colors of individual objects/faces I'm trying to apply the GI on.

Right now I am only able to get color of the surfaces from the original image, which is ok in actually lit scenes. But for correct color mixing I need to know diffuse component of each surface I'm bouncing the light on, so I can light up even objects that are fully shadowed (black) without it.

I'm reading everywhere, that "_CameraGBufferTexture0" serves this purpose. But when I use this, shader complains about undeclared variable (quite reasonably). If I declare it as "sampler2D _CameraGBufferTexture0;" and then read "tex2D(_CameraGBufferTexture0, uv);" the result is always grey color. So I am guessing I am missing some key info here, maybe these names are old - used with the "CG" includes, and current HDRP when working with "HLSL" includes uses different ones, or I need to pass them myself from the postprocess .cs side?

 

After another few hours of searching, I found this post by @bgolus
https://forum.unity.com/threads/accessing-deferred-renderer-g-buffers.315223/#post-5078510

Sadly all my tests to get to that buffer were still unsuccessfull. I tried all declaration+sampling possibilities I could think of, but none of
TEXTURE2D_X(_GBufferTexture0); + LOAD_TEXTURE2D_X(_GBufferTexture0, positionSS);
TEXTURE2D(_GBufferTexture0); + SAMPLE_TEXTURE2D(_GBufferTexture0, s_linear_clamp_sampler, uv);
sampler2D _GBufferTexture0; + tex2D(_GBufferTexture0, uv);
didn't seem to do the trick. Honestly, I'm just trying stuff at random at this point, but still no luck

Edit: Surprisingly, I get some results from _GBufferTexture1 (which should be for specular color?), but _GBufferTexture0 is fully black.