Some thoughts:
Since you already have seperates and are comfortable with those, I'd just stay that course for now.
I would hang on to that XL-280 for now. If you like to play around with solder, there are lots of upgrades for the various hafler amps. I started with a DH-200. There is a longer story but in short, I got some great performance using the hafler and a CJ FET pre feeding some refreshed infinity RS6Bs. My DH-200 was modified with caps and precision resistors by the previous owner.
The Denon is a decent enough unit. If you were going to replace it, you'll need to find something with an integrated phono preamp or buy an external one. You should keep your table if you still have vinyl. There is a CJ SC-1 on agon right now (
http://cls.audiogon.com/cgi-bin/cls.pl?preatran&1213695788). It's an older unit, predating the SC25 I had paired with the DH220. If you feel like trying something along those lines, I would offer the seller $200 but not more. Don't be ashamed of offering less than what people list, some people have an inflated sense of worth regarding their gear. I sold my SC25 for $250 without the phono preamp module (phono pre would have added $100). Another option would have been this CJ PV2Ar (
http://cls.audiogon.com/cgi-bin/cls.pl?preatube&1213309273) if it had not gone so quickly. The PV2Ar is one of those classic pieces that just don't lose value. They have actually been going up the last few years. I originally heard one with the DH-220 and it was really nice but I went with the FET unit because I was scared to try tubes at the time.
The ADS L620 are probably more than 20 years old now. If they have not been rebuilt, they are probably the first thing I would consider trading. There are other monitors, but I really like the von schweikert stuff right now. The VR-1s come up less often now and seem to sell pretty quickly. I think they are discontinued. These
http://cls.audiogon.com/cgi-bin/cls.pl?spkrmoni&1213369135 went for $600 as new but I've seen really nice pairs go for $450. You have to be patient and ready to jump when they come up. Some people here have them and can comment on how they sound.
How are you playing your recordings now? If you make CDs, does your transport have an SPDIF out? You might find that even a moderately priced outboard DAC could make a big improvement. The CAL alpha is a great DAC for 16/44 (
http://cls.audiogon.com/cgi-bin/cls.pl?dgtlconv&1213309405) and you could use it for some time before needing to upgrade it. It has a tube gain stage so you can tube role. CAL is out of business but some of the people from CAL are still around and servicing these. I had a Sigma for years and never had any issue with it. The ad doesn't say if this one has the 24/96 upgrade but I read some reviews that the stock one sounds better than the upgraded unit. Only issue with this one is the seller has no feedback and there are no photos so I'd proceed with due caution but it is a good price on a very sweet DAC. There is also this Musical Fidelity unit (
http://cls.audiogon.com/cgi-bin/cls.pl?dgtlconv&1213068426) but I have not tried it, just their headphone amp which I like. Either of these DACs would last through a few other compoent upgrades.
In your case I would probably go speakers, DAC, preamp and then reevaluate. Note that I recommend from a limited number of makes because those are where I have experience. Other people have wider experience and can provide a wider range of options. Also check out nickspicks for reviews.