I love Sefa's work too! I've listened to both Da Tweekaz and Sub Zero Project however Phuture Noize tops the charts for me when it comes to atmospheric hardstyle. I often listen to rawstyle too - mostly Radical Redemption and E-Force.
Do you listen to any other genres apart from Hardstyle? I dabble a lot into atmospheric or hard techno myself. Have a listen to the songs on my profile and you'll see what I mean!