I tried it out both ways last night with my (very) old Vandersteens and the high pass had obvious benefits in both cleaning up the midrange integrating the sub.
I also found that my plans to improve room acoustics are badly needed because quite bit of equalization was needed to flatten out the LF.
I had some noise/degradation, but I was using extremely crappy interconnects (hardware store quality) because that is all I have in long lengths.
The benefits look big enough that if I end up with speakers that like the HP this much, I will probably subtitute a high quality HP like the Vandersteen 5m-hp for the Velodyne HP. Then, I can use my shorter current higher-quality cables (with one addition) also.
I guess that what I am saying is that I am not going to throw in the towel if it turns out that the velodyne HP is not up top snuff. Another advantage of skipping the Velo HP is that I can then attenuate the input to the Velo - I'm running at volume 3-5 out of 100 now with 2-channel.
All of this won't matter if I end up with the Merlins since they have a built-in HP at 28 Hz as part of the Super BAM and others have had good lucking integrating them full range as they stand.
Please keep adding comments. I consider this to be an important discussion since we probably can't buy a floorstander that is clean to 15 Hz for less than about $20,000, if that. Personally, I also value the ability to use the sub for HT with a totally different set-up.
Also, I could not identify the source of the bass whatsoever with just one sub. I was using a very steep crossover, though. I am perfectly happy to add a second if it can be demonstrated that I am missing something.