Whatever you do, there are fairly easy ways to test the bass routing with the Ultra to check & reassure yourself. For me, the best was to download an Android tone generator (e.g. "PA tone" is simple and add-free), cast my phone audio, then play with various frequencies. You can tell where the bass is coming from even at low volumes by touching the driver or the port of a speaker, then use a cheap sound-meter with C-weighting to equalize levels.
For a 40hz speaker 60 Hz sounds like a good crossover point. If you have room issues (say at 70 Hz) that are easier to control with sub placement, you could go higher. Once you have the levels matched, it's easy to play around and see what sounds good.
PS The bass mgmt is a big deal IMHO; I see in the other thread you're wondering if it's worth it but I wouldn't consider a system without it now that stereo components like the Ultra exist. Even for music only, it frees you from
having to use floorstanders in the future, among other things. Whereas, analog preamp is only worth it if you have analog inputs -- the distortion of digital inputs is almost universally worse because it's just easier to have high-precision analog components in a DAC chip. In my case the Ultra replaced a $$$ processor as part of my downsizing to 2.1, and it's very likely better. I can't honestly tell a difference but I know how that prepro measures (significantly worse) compared to pure DACs, including the Pro Plus which I expect the Ultra to improve on sligthly.
If you're lucky, your analog volume control is equally transparent and you're dealing with sighted bias (you "know" this component should sound better going in). If you're unlucky, it distorts slightly but in a way you like (like those tube preamps my dealer keeps trying to sell me), in which case your road to audio happiness might be considerably longer