I am making a concept album LP thing with my band. We have run into a problem. We are trying to make one specific song have a sinister sound, with a sense of doom. We want a really huge sound. Our problem is whenever we try to make it sound more sinister it ends up sounding too much like a metal song. We were aiming for like a cross between Pink Floyd's "The Trial" (https://youtu.be/FCMHmDnfD6I?t=4m15s) and the end of the Beatles' "I Want You (She's So heavy)" (https://youtu.be/n4vHWnTMc9Y?t=6m30s)

I need tips for writing this song. Anything will be helpful.
The most sinister albums i know of are.

Bohren - geisterfaust
Actually nothings more sinister than that..l

Keep it slow, be unpredictable (random jarring stops) odd sounds.
Go out of key, major chords in the right/wrong place can really work wonders.
Also use diminished and augmented chords and scales.
A repeated phrase can be twisted if you do it over and over, then change it when you have created a false sense of security.
A sudden blast in a soothing quiet interlude can take on the characteristics of a jump scare.

Tupelo by sikth is a good one too.
And dont forget the imperfect cadence.
Try listening to and with her came the birds
Oh and...
Never disclose the horror, lyrically be as obtuse as possible. In a horror movie when you finally see the monster or whatever all that suspense fizzles away.