Straight XLR vs XLR to RCA adapter

I think you are referring to the possibility of using adapters at both ends of your RCA cable. That would definitely not be "doing it right," for several different reasons.

I would emphasize, though, that the tradeoff between RCA and XLR interconnections will often be more significantly influenced by the internal design of the components that are involved than by the cable itself. So it might be helpful to first try a pair of inexpensive but well made balanced cables, such as Mogami Gold Studio or Blue Jeans, before deciding on whether or not to invest in more expensive cables.

Regards,
-- Al

Defeat the purpose of what ?? If you are talking about preamp gain, no it does not.

This will depend on the equipment. If the electronics are fully balanced throughout then your best cables will be XLR to XLR but if the equipment is not a true balanced design than it is not a big deal.
Contact the company and find out if your equipment is 100% balanced.