That does look like a strong contender. I have some more goo I want to farm up soon and I'll give it a spin myself.
I think a 2 item swap is really not much of a burden, but I'd quibble that the
Giantcraft armor is BtCoA so that's not ideal on a throwaway character IMO. I'd probably use something BtA like the
Crimson Chain from the P2P Lordsmarch chain which is easy to farm if you own the content, albeit not as good as the Giantcraft. A
Parasitic Breastplate upgraded with Reflex +10 and swapping the PDK trinket for a
Symbiont might work out really well and it's all BtA, but that is a lot of farming if you don't have them already.
I'd like to find some way to add a Devotion item, such as the
BtA +42 Devo ring you can get almost instantly by rolling a throwaway Vet2 Cleric. Unfortunately the PDK rings are strong for this build (CHA, DB, poison saves) so that's not a permanent option, but it might still be worth having a Devo ring as a swap item. I think that any of the default trinket, goggles, or belt could be swapped out without costing too much (although enhancements might need tweaking to force an even stat). Anyone know of any easy to get Devotion options for any of those slots?
Are you really having much success getting Soundburst to stick without any DC improvements? CHA should be 24 (=16 base + 1 SS enh +6 item + 1 exceptional), so the DC should be 19 (=10 + 2 spell level + 7 CHA mod), and Fort saves tend to be high on mobs so if you are running challenges at a higher level that seems a stretch. Plus it has a Spell Resistance check and there are lots of SR-endowed Drow and Demons running around. Although maybe I'm just jaded from running hElites with their over-scaled saves and underestimating it.