Just ordered a Helix LT and would like to know which IR's are you using with it. From the reviews I've read it seems that the stock IR's don't sound as good as external ones.
I suggest giving the stock IRs a chance, manipulate the mic position and run dual cabinets, same cab with different mics and positions. They are surpsingly good. I have Celestions, Ownhammer, RedWirez, etc at my disposal and the stock cabs can absolutely be dialed in to sound as good. whatever reviews you read were people who didn't spend enough time with the stock cabinets.