Well that's not the discussion, here, really. The discussion is whether Jesus is God or not. And He most assuredly is. In Hebrews 1:8-9, the writer is directly quoting from a Psalm (45:6-7) which extols the Davidic king, and only Jesus, as the Davidic Messiah -- the annointed One -- truly meets this description, since by reigning at the Father's right hand (Hebrews 1:3, 13) He possesses an eternal kingdom forever and ever and reigns in true righteousness (Hebrews 4:15, 7:26-28). The messianic Son is rightfully also called God, in this case by God the Father in Psalm 45:6 and thus Hebrews 1:8 -- as in John 1:1, 18... John 20:28... Romans 9:5... Titus 2:13... and 2 Peter 1:1.
To your statement, though, Hebrews 1:8 absolutely does indicate that God is at least a duality.
Grace and peace to you, Tigger2.