Can you tell us about your listening room...size, furniture, acoustic treatments, type of floor?
I would always pick the alternative that goes with subs. There are many good reasons, but one of the main one's is the ability to put an EQ in line with the subs. That plus a high pass filter will almost always give you the chance to get better overall bass response in a room than trying to get the same from just two large main speakers.
Then there's a litany of other benefits, like increased dynamic range, lower main amp stress... etc.
I recommend the use of the AM Acoustics room mode simulator to help you place your speakers and listening location, careful measurements and GIK soffit traps in the corners if needed. If you do all this well you are going to have a very difficult time finding a system that performs better in bass speed, impact or system dynamic range and clarity.
That's a really large space that you need to fill and pressurize. Couple of thoughts beyond the good thoughts from @erik_squires and @tomcarr
1-Going with the Main + Sub combo will give you options to move the subs around the room and tune the bass. If you love the sound of the Mac integrated this is probably the way to go
2-The larger B&Ws will push the limit of the integrated without subs. You may need more power to keep the bass clean esp. at louder SPLs.
3-If you really like a full bottom end and a properly pressurized room the RELs might get you there or they might not. You may want to consider the JL Audio Fathom line of subs. They have 2x the power and more usable output then the RELs. They are known like the RELs to be very musical and two channel friendly.
4-If the porcelain floor remains mostly uncovered the lively top end of the B&Ws will become even more so. Will you be happy with that sound? Good luck and cheers.
801D4....Also, the McIntosh has plenty of power to drive them. You can always add subs later if you are not happy with the bass output. I had a pair of 802D3s and powered them with a Naim Uniti Star in a large room. The bass was adequate but then moved to a CODA 16. The presentation was much better albeit at a significant cost. I was amazed at what the Naim did though in that large of a room.
Subs always subs. electronic music can only be played properly with subs…. Not kidding.
Anyway, I listened to the 802D4 on McIntosh Mac611 mono blocks and McIntosh 2700 tube preamp. It was ok, the bass was fine, no major complaints, mids were a touch thin (tipped up a bit). Then I came home and listened immediately the same songs on my Revel 228be, McIntosh MC462, with two JL E112 subs highpassed at 60hz. Honestly my much cheaper system was better, much better. The bass was well beyond the depth, quality and slam the 802d4 without subs could not touch. I also think the Revel are more natural/smooth sounding but they do give up some detail next to the 802D4. I would expect the 801D4 to come up short next to subs too.
Personally 801. I much prefer completely coherent sound across the spectrum. B&W has put a huge amount of effort into making these things the best they can… flat to 15hz. Why add subs to the mix when they are unnecessary.
Also, from the aesthetic point of view, single towers are much more elegant. I remember finally getting rid of my subs… both from an aesthetic and sonic perspective… a much cleaner and more elegant solution!
May I suggest that you go to the next step above B&W. The engineer responsible for most of the finest technologies at B&W left when B&W was sold and eventually formed (with a partner) Vivid Audio. Vivid has refined these technologies and taken them to the next step. Rather than a B&W 801 D4 ($35K) or 802 D4 ($14K) with subs, go with the Vivid Audio Kaya K45 ($19K), K90 ($28K), or Giya G4s2 ($34K). Regardless of what specifications might tell you, the bass response of each of the three models is simply amazing. These speakers offer another level of transparency, detail, and the ambience of the recording. If you had been considering the B&W 801 D4, you should here the Vivid Giya G4s2. Next level performance.
801D4 - you can add subs at any point later on if you find you need more bass.
Although the 802D4 shares the same midrange enclosure and tweeter as the 801D4, Bowers has done some magic on that xover, midrange driver, and woofers to separate it enough from its lower sibling. The 801D4 when i auditioned it had a much effortless and fuller sound. Besides the deeper bass it was the midrange that stood out enough.
Both the 801 and the 802 will benefit immensely from subs. You are not just getting a speaker, you need to marry it to a room. The optimal location for imaging and so on is usually never where a sub bass driver oughta be. So, any speaker will benefit from subs (full range or not!).
That REL is not the brightest idea for your use case. Consider the ELAC Varro line, especially the DS1000 dual force balanced 10inch for your use case....and it is cheaper than the REL, how about that?
Well, in your use case
a) Sub driver size is much more closely matched to the bass drivers on your speaker. If you don’t have servo control (from the likes of Rythmik), this is an important factor.
b) The Elac Varro will give you extension out the wazoo, dig into 14, 15hz, without blinking (something your Rel mentioned above can never do). You will perceive things in tracks that you would never hear otherwise, i.e. in a sub with weak sauce extension.
c) The Varro line comes with a very unique auto-calibration feature that is extremely beneficial for 2 channel purist systems without any PEQ or whatever else. It was pioneered by Andrew Jones when he was still at ELAC. At minimum, the calibration will match the sub’s response right at the driver to your listening position, even if a user knew diddly about how to integrate a sub. In other words, it will nullify the room’s confoundance with just a simple bit of positioning and running the cal. It will also give you several bands of manual PEQ, delays, etc/whatever else for more advanced users.