Clew- Agnes3 has the right idea. Tubes and ESL can be outstanding together. As was suggested, you could take this in steps by getting the tube amp first, utilizing the Denon pre outs. This would get you on your way. (You might look into a nice used VTL stereo or mono-blocks amps. I saw a pair of ARC M100 mono-blocks for around $2K not too long ago. I've seen the Cary V12 used as low as $2200, and it is extremely good. Plan on spending $1500 to $2K to get good build and sonic quality. Budget a little for some New Old Stock (NOS) tubes, and you'll be very pleased with what the M-Ls can do.
The next step (and equally as important) would be a nice analog pre-amp. Again, I'm partial to good tube designs. (An older Audible Illusions 2D can be found for around $500, and it has the added advantage of offering a very nice internal MM phonostage if you decide to explore the beauty of vinyl). C-J, MFA, Aranov all offered fine amps and pre-amps that at used prices can be excellent building blocks. Also, there are several manufacturers making excellent components selling factory direct that offer very high value. Wright-sound.com is one such site, and there are many others if you really start to investigate the net.
Though I've mentioned the obvious components, don't forget about interconnect and speaker cables, power cords, and what the equipment is resting upon. I recommend that you check out the Sonoran cables and Sistrum/audiopoints at audiopoints.com, as I've had excellent results with their products. Nearly everyone will have their personal favorites, and I'm no exception.
You are just starting your journey to the dark side ...er, I mean the enlightened path of hi-end audio;^) Keep in mind that most of the fun is in the trip, not necessarily the destination. Enjoy!