Could you make this any harder 🤣
That's the trouble, the Domane may not be as quick as the Emonda but for many it is quick enough, like wise the Emonda may not be as comfortable as the Domane but for many it's comfortable enough. In your case when someone requires a bike for "max effort for short periods" that would normally result in them choosing the Emonda.
SL6 in both models are in short supply mind you, Trek have no stock of either but you may find a dealer who has one that they bought as part of their stocking in pre season order in that size. The 56cm Emonda in both colours are May 2021 and the Domane are quoting September which probably translates to them then being the 2022 models! Sadly this is consistent with many bikes from popular manufacturers, demand has far outstripped supply.
At the moment dealers are pretty much trading off their pre season deliveries and as such they may still have some Domane's and some Emonda's to offer, even if they are not the SL6 model in that size. When these initial deliveries sell through and with such long lead times for the replacements it's not surprising that many stores are anxious about what the short and mid term future holds. In normal times some Trel dealers can offer a
bike fitting service, their
fitting jigs will give you an indication how each will 'fit', not only will that help with what size to choose but it also helps with model choice.