I believe your cable combination will work, BUT you must ask/ensure that the female DIN->RCA is wired for Powerlink and not AUX in (or out).  Alternately, if you have an old DIN male Powerlink to RCA "lying around" (from some older setup) then your B&O dealer can supply a short RJ45-to-female-DIN cable, even though the website only shows RJ45->DIN-male.

Your comment about using a BeoAmp2 to power the subwoofer seems misguided because you say above that it is a *powered* non-B&O subwoofer.  Maybe it has both line-level and speaker-level inputs?  In any case, letting the sub's own amp do the work seems wiser.

Building your own RJ45->RCA cable is not impossible, but it's fussy if you have never done so before.  You must use a shielded RJ connector -- which has a special crimper tool -- and run the shield to the ground on the RCA, plus not just some wire but actual foil or braid thru the length of the cable -- typical for running line-level audio around (and what was done inside the B&O cable you already own).

Thanks for the response.  I really appreciate your input!  I will reach out to my B&O dealer and see if they can provide a short shielded RJ45 to female DIN cable.  If I can get that, there are several higher quality male DIN to RCA cables available that seem to be pinned out correctly to meet my needs.

My main profession is IT work.  I do own the correct tools to crimp shielded cat 7 cables and I'm very comfortable with that process.  I also own soldering equipment, but I don't have much experience with it and to be honest, I'm just not very good at soldering.  I would really prefer purchasing a high quality professionally made cable if at all possible.

I understand your concern about bypassing the amp on my powered subwoofer.  It wasn't difficult because I built the subwoofer myself.  I'm a fairly competent wood worker and I've dabbled in building speakers and subwoofers over the last 30 years.  About 5 years ago I started using CSS SDX12 XBL2 12" Subwoofers.  In a properly built sealed enclosure, I haven't found another subwoofer that provides such clean, fast and crisp sound without being overpowering like most subs are.  This particular subwoofer doesn't really shine unless it's powered by a 1000 watt amp.

If I can't find a good RJ45 powerlink to RCA cable solution I'll probably just go with a BeoLab 19 sub. I have heard the BeoLab 19's and they are good, but they just don't seem to deliver the impactful bass that I've grown accustomed to with my 12" CSS subs.

Just a quick update.  The B&O powerlink RJ 45 to Din (male) connected to the Atlantic Computer Tech female Din to RCA cable did work to power my subwoofer.

I installed four in-ceiling height speakers this weekend.  The bass coming from those new speakers, along with my side speakers and the Theatre, is pretty solid even without the sub.  After I add a pair of front speakers and a pair of rear speakers, it will be interesting to see if a sub is even needed.

Thank you for following up, so others know what worked!  (This forum has no ratings/scores to give the post a "thumbs-up".)

I'm happy to contribute at least a small amount to this forum.  Living in Wisconsin, since there are no B&O dealers anywhere near me, I've been making my purchases from a reseller in Arizona and from Sound-Affair in the UK.  I do have two B&O integrators that are within 100 miles of me, and I've reached out to both of them and offered to pay directly for their services.  Neither of them have ever responded so I've had to figure things out on my own.  This forum has been my best source for finding answers and I'm very appreciative that it exists!

On another note I did end up purchasing a BeoLab 19 last Friday.  James from Sound-Affair found me a reasonably priced unit in the color I was looking for and it arrived a few days ago.  I've spent the last 2 days with both the BeoLab 19 and my own 12" sub connected to the theatre, running just one at a time to test the differences.

For movie watching, the 8" BeoLab 19's performs very well and I can't say that I hear a real difference between that and my 12" sub.  I am impressed with how hard this little sub hits when watching movies.  It more than meets my needs.

While listening to music, the BeoLab 19 does get low, but it's just slightly less impactful than my 12" sub.  In the Listening Position / Bass management / Redirection level I have my 12" sub set to -15db.  At that level the bass hits nicely, without being overpowering and without ever rattling anything in my room at a relatively high listening level.  I left the BeoLab 19 at +3db, which is where the automated room calibration placed it.  At those settings both subs get down low enough for me, but the impact just isn't quite the same with the 19.  If I boost the 19 to +6db it gets very close to my 12" sub, but it also starts rattling some items in a nearby cabinet.

For now I've moved the BeoLab 19 back to the default +3db setting, I moved my 12" sub back into my wood shop, and I am very pleased with my Theatre's overall performance.  Although I hate to admit it as a somewhat competent woodworker, but I have no chance whatsoever to make a sub enclosure that is anywhere near as beautiful as the BeoLab 19 is.