I will only have about 5 inches of breathing room up with the 219.Hmm. Both amps are specified as consuming 400 watts of power. (Although I’m a bit surprised that the 219ia isn’t closer to something like 300 watts, or even a bit less). Nearly all of that power will be converted into heat, and radiated directly upward. Hopefully that space is open at both the rear and the front, and hopefully the material that is above the amps is heat resistant (and won’t conduct the heat into a component that may be above that surface). Otherwise, and possibly even given those conditions, I would have significant concern even with the 10 inches of clearance you would have with the 508ia.
Best regards,
-- Al