What’s the rest of the equipment in your system, and do listen to 2-channel too and if so how important is that to you vs. HT.
In this case, upgrading your subwoofer is not about adding volume to the system, although that will probably also be possible. A larger subwoofer should allow you to reach lower in the frequency response range to take advantage of the LFE track on your multi-channel AV entertainment, as those tracks can get well into the infrasonic range. This is less important for music that is based on natural instruments (pipe organs notwithstanding, since they can get down to infrasonic frequencies), but if your music tastes run to music that includes synthesizers too, those lower frequency ranges that an improved subwoofer can reach can be applicable here too.
It's worth noting that while CEA-2010-A measurements for the base B&W AS610 have not been taken, nor are they comprehensive indicators of a subwoofer's performance, the ASW610XP has been measured, and its performance here is roughly analogous to the ubiquitous SVS SB-1000 Pro subwoofer. I would suggest that while the DB4S would be considered an upgrade from your current unit, there are other options to consider. Several non-B&W products might gain you equal or better performance for the same budget, particularly if you were to invest in a pair of subwoofers rather than a single larger unit. I have been particularly impressed with the output of both Monoprice's current-generation THX subwoofers and RSL's Speedwoofer 10s/12s, both of which are available at prices under $1,000. Dual subwoofers, properly placed within your listening area, can provide dramatically improved bass response within it, regardless of the volume they are set at.
While it’s not an apples to apples comparison, I recently replaced a 30 year old Paradigm PS1000 with a very nice used B&W ASW855 for my second family room system. I have an SVS PC12 in my main system which performs respectably, but this B&W is mighty impressive. It is effective down to 15hz and seems to outperform the SVS in most, if not all, aspects. If you can find a good used ASW 8 series it may do well with your other B&W speakers.
@hawkrider00 Well the 855 damn well should outperform the PC12 — you’re comparing a $3k sub to a $950 sub and inferring B&W subs are better. Apples and oranges dude.
@hawkrider00 Here are two reviews from the same time period that quote the retail prices as $3000 and $949 for the 855 and PC12, respectively. Either way, to say the 855 outperforms the PC12 is, well, duh.
Even at $2200, for that price you could get two SVS SB3000s. Now that’d be a more interesting, useful, and relevant comparison and truly apples to apples.
They might? The middle of the room next to the speaker location is typically within the rooms null. -6dB sub-bass speakers dramatic roll off seems to allow them to work within room nulls. The crossover might be the first adjustment in blending with the satellite pair.
-3dB subwoofers lowest frequencies struggle when placed in a room null. Subwoofers usually give their most detailed performance and disappearing when positioned within the rooms greatest standing wave bass mode.