Bigger Amp?

The HT Pro Silways introduced too much shrillness/brightness/sibilance into my system. The Truthlinks were a lot warmer sounding at the expense of some rolled off highs, but worth it to me. I currently use something else, but possibly you could experiment with some different cables before changing gear.

If you like the overall sound of the McCormack but want to make a significant upgrade, you might try the SMc Audio upgrades. I went from a 0.5 DLX to 0.5 Rev B and the improvement was very significant, across the board. You might want to talk to them about your associated equipment. Another thought, if you are using the Theta as a digital volume control, others have reported loss of dynamics and overall "thin" sound when using digital sources without an active pre-amp. Maybe try borrowing one and see if it helps (tube pres work well with McCormack amps; I am using a BAT VK3i).

Try experimenting with different upgrade AC cords; there's no mention of cable tweaking above so I don't knoiw if you've tried this yet, but never underestimate what cables & tweaks can do for you. You'll never know the full capabilities of your existing equipment until you thoroughly investigate further. Might already have all that it takes, but you just don't know it yet...