You can always turn a sub down if you still find it too loud. The AV receiver will do its auto-setup-wizard thing. You can then either go into the AV receiver menus and dial the sub down or use the volume dial on the rear panel.
What you can't really do is turn up a weak sub to 11 or magic it some extra depth or precision. They work to their limits. Pushing them beyond is when things get messy, boomy and just unpleasant.
You came on with a plan to spend £400-ish on a one or the other 8" sub. We looked at them and told you they are pricey for the performance. We suggested a couple of alternatives, and that saved you from making an expensive mistake.
Quick question: did you pick those out, or did RS staff recommend them?
There's a lot of knowledgeable folk here in the forum; people who have been into AV and music for a long time and gained a lot of knowledge. What's more, no one here has any vested interest in whether you buy or not. We're not the ones selling you the gear. We make no profit nor take any commission. You might want to keep that thought in the back of your mind when you're next talking to the store staff.
What we've done for you is pick out what we think of as the best subs from the whole market, and not just what shop A or shop B happens to stock. That's impartiality for you. These are what we'd buy if we were in a similar situation to you. Here's the thing though; none of us are you. What you finally decide is up to you.
Is the W10 6G a bad sub? - No. Monitor Audio is a decent brand and I've sold and demoed more of their gear than I can remember. I've always liked the Bronze series for its sense of fun and value. They're making complete packages including subs, and those subs compliment the main speakers nicely for music, and they do okay for movies too.
Was the W10 6G the best sub you could buy for £625? The simple answer is no.
Is it any better a deal now that it's on clearance at £450? Yes, quite obviously. It's £175 cheaper.
Does this make it the best sub you can buy for £450? I'm afraid that the answer is still no.
Is it the right sub for @arix ? If you want to buy from a retailer and feel like you're getting a deal..... then maybe. Would I run a W10 6G at home? Yeah, sure. Would I run it in preference to a P12-300 or a s/h SB-1000 Pro.... er...No. As a sub to match the visuals of a set of MA Bronze speakers there can be no better choice. But if I'm not using the matching MA speakers, is there a compelling reason to choose this sub? The honest answer is no, but your mileage may vary.