I have done a fair bit of experimenting with DQ's, which are IMO still very competitive with many current designs from an overall "listenability" perspective. I've found their main weaknesses to be somewhat "soft" highs and a bit of a suckout in the low mids.
If your budget is fairly limited, my recommendation would be to spend the money on addressing those issues with better mid/tweeter section caps and skip, for now, any changes to the woofer side.
The low end exhibits a bit of rolloff in comparison to many newer speakers simply by virtue of it's sealed enclosure vs. the trend toward ported "boom boxes", but it IS tight and melodic - as long as you're giving them plenty of power. So I don't think you'll see much improvement there by replacing caps - and it's certainly not where the bang for the buck is on a budget. If you're happy with the mid/high upgrades you could later contemplate replacing the old Advent woofers with something more state of the art.
One additional tweak to consider if you're running them with grills on is to damp them by placing a "quasi-triangular" strip of Dynamat along each side of the grill (on the expanded mesh inside) from the top down to just above the woofer enclosure. You want to keep the Dynamat's shape as wide as possible without "interfering" with the tweeter and midrange drivers' normal horizontal dispersion patterns.
Then place another strip across the grill near the bottom (well below the woofer). Then glue thick felt onto the dynamat to prevent acoustic reflection.
The DQ grill was a cosmetic nod to the Quad's design, which was a favorite of Jon Dahlquist, but it's a sonic problem that serves little purpose other than look cool (although it does protect the speaker really well from toddlers). Doing this mod will significantly reduce coloration in the mids and highs, and allow more bass energy to propagate rather than be absorbed.
If your budget is fairly limited, my recommendation would be to spend the money on addressing those issues with better mid/tweeter section caps and skip, for now, any changes to the woofer side.
The low end exhibits a bit of rolloff in comparison to many newer speakers simply by virtue of it's sealed enclosure vs. the trend toward ported "boom boxes", but it IS tight and melodic - as long as you're giving them plenty of power. So I don't think you'll see much improvement there by replacing caps - and it's certainly not where the bang for the buck is on a budget. If you're happy with the mid/high upgrades you could later contemplate replacing the old Advent woofers with something more state of the art.
One additional tweak to consider if you're running them with grills on is to damp them by placing a "quasi-triangular" strip of Dynamat along each side of the grill (on the expanded mesh inside) from the top down to just above the woofer enclosure. You want to keep the Dynamat's shape as wide as possible without "interfering" with the tweeter and midrange drivers' normal horizontal dispersion patterns.
Then place another strip across the grill near the bottom (well below the woofer). Then glue thick felt onto the dynamat to prevent acoustic reflection.
The DQ grill was a cosmetic nod to the Quad's design, which was a favorite of Jon Dahlquist, but it's a sonic problem that serves little purpose other than look cool (although it does protect the speaker really well from toddlers). Doing this mod will significantly reduce coloration in the mids and highs, and allow more bass energy to propagate rather than be absorbed.