@ifsixwasnin9 I believe the 690 is 2.5 way design. I bet they would work great with your existing Yamaha. (Forum member
@Danzilla31 owned a pair of 698 and is another "bass head".
![Wink ;) ;)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
He could give an honest opinion on the bass performance of the 698.) It is very good value for the money as it uses some technology from the higher end JBL HDI line and looks very similar. You might find it interesting that TLS Guy thinks that the 2.5 way design of the 690 is better than the 3 way design of the 698, and the 690 is $100 cheaper.
While your Yamaha does not have bass management, it does have bass, treble and loudness which a lot of modern gear lacks. Something with bass management and room correction software also often requires a TV to navigate the menus, so if you want bass management without video support the choices get limited. If you're thinking of upgrading your amp later I suggest you get some recommendations here on the forums.
Downfiring sub is not necessarily bad. My first sub was downfiring and my current one fires forward. Have you tried turning up the crossover on the Monoprice as suggested and playing with the levels?
If you sell the Monoprice, you may find something like the 690 would work fine without a sub. JBL rates the 690 down to 36Hz so it's a pretty full range speaker. If you still want a sub I would state your budget and get opinions here. There are fewer options available at the cheaper end of the spectrum but there are some decent performing subs that don't cost a fortune. The really good ones start at about $800 like the RSL Speedwoofer 12s. Here is an article on subs in the $500 range:
https://www.audioholics.com/subwoofer-reviews/best-500-subwoofers-2023
Erin's Audio Corner looked at some cheaper subs a couple of years ago (in the $250 range):
Given the age of your current JBL speakers, though, I would recommend considering an upgrade. TLS Guy is one of the most experienced with vintage gear and his analysis is usually spot on. If you're patient, JBL is known to have some really good discounts on occasion so you might find a pair on sale.