I heard back from Line 6...this was their reply:
"The feature you're describing is something that is found within our HD500X or the Helix. However, it is not available within the Firehawk 1500 or Spider V. Since you have Variax guitars, I would likely recommend the Helix more so over the Firehawk 1500 - but both of them come with the Variax connection."
Needless to say, I was rather disappointed in this answer. Not only is this feature almost free to include (from a programming standpoint), its usefulness can't be overstated. Anyone who has used the feature would never want to go backwards, and those who haven't probably just don't know that it exists (I've talked to a few HD500 owners who had no idea they could do that). Also, a huge problem with his suggestion is that Helix is not an amplifier. One of the big appeals to me of the Spider V and Firehawk is that everything in my rig except the guitar is contained in one relatively small and easy to set up box. Not to mention that Helix is quite a bit more expensive, which is probably why it was suggested.
I've been a long-time user of Line 6 products (POD HD500 and two Variax guitars). I personally have had good experiences with them. However, I know people personally who have had nightmare experiences with Line 6 Support, resulting in the loss of hundreds of dollars. I have noticed the Line 6 customer experience declining rapidly over the past few years, and it seems to continue to spiral negatively. To offer a brand new product like Spider V without this simple feature (not to mention without an effects loop and Variax support) is a sign that they care very little about their customers' needs...and I think it will cause them big problems in the future.