@Buckeye_Hydro is definitely the expert here so I will defer to his opinion.Hey Jayjay, my set up is fro tap to sediment filter, to carbon filter, to RO, to post active carbon filter, to deionization filter. Let me see if i can upload a pic of the set up, its almost like the HbrewO but just my take on it i guess.
IMHO, I believe you can just take out the deionization element, it's simply not needed for brewing. If we were on a forum about maintaining reef tanks with hard corals and their extremely demanding water requirements it would be useful; for home brewing it is simply overkill. That being said if you are making adjustments to your water before brewing with mineral salts, the DI won't hurt and you can be assured in assuming your ions really are at 0-0-0-0 in your water calc. Just don't drink the water, only use it to brew.