Sorry about the delayed reply, Mr Bassman...
But a glitch in Line 6's server upgrade had some of us "locked out" for over a week.
My comments arise from me being an old sod who's been priveleged to have spent over forty years recording and broadcasting everything from live opera to Sesame Street.
Folks who haven't actually stood in front of a "profundo" bass vocalist won't really "get" your enquiry, which is that you're after the silky bass detail you've been hearing in recordings of your voice made with the likes of AKG's CK1/CK5 and Neumann KM84/85 capsules, no doubt positioned "out front" on their skinny extension tubes.
(I've been lucky enough and am old enough to have experienced both Paul Robeson and Ivan Rebroff, so I guess you and I are "singing from the same hymn sheet".)
The bad news ?
NO capsule that you can screw onto anybody's transmitter will work like those you've mentioned.
The good news ?
You own one of the few systems (at any price) that CAN deliver the full authority and detail of your bottom octave, from in your hand (or on your stand) all the way to the mixing desk, but achieving this will require you to master the art of manipulating the mic's proximity to your mouth.
Varying the mic's distance from your lips must now become an intuitive extension of your expression technique, as automatic as breathing.
(By way of illustration only, check out YouTube clips of Ella Fitzgerald manipulating the distance of her trusty old SM58 ...and please forgive me if I'm telling you what you already know.)
More good news.
I really can't see much point in parting with cash for other capsules, unless you strike a foldback monitor situation that demands a particular polar pattern, or have a proximity technique that you've long established with a certain favourite mic.
My feeling is that you should try to borrow a small mixer that can feed your XD-V75 receiver into high quality headphones, so that you can spend quite a few private hours experimenting with mic models and proximity technique.
Unfettered access to a "PortaStudio" type recorder (or recordings into a laptop) would be even better, as "coming back" to recordings as a less-involved "normal" listener makes comparison much easier.
I'm betting that the unprocessed and natural bass detail you'll hear from some mic models will be a revelation, your next challenge being to ensure that it isn't lost through "we always set the board like that" routine processing by venue staff !
For your information, when it comes to "basso profundo", my old ears slightly favour Line 6's model of E-V's neodymium-magnet 767 over their AKG D5 and Sennheiser e935, but the individual voice is all important and (as ever) there's no "correct" answer.
Thanks Ron. I did find once I was hooked up to our full stage setup that I was amazed at the sound I could achieve with the L6 capsule. I do love the 767 sound but found in sampling through all of the models that the 935 gave the most pleasing results through the full range of my voice. I can't say enough great things about this system I am amazed. I am trying to share it with others in my circle to try and liberate them that shure, sennheiser, and audio technica are the only thing out there. Thanks again.