I built both a DH-200 and a DH-220 from kits back in the day and was satisfied with both. As bpoletti said they are very similar and in fact, are nearly identical. I thought the 220 sounded just a smidge more full but never had the urge to modify either of them. Both are extremely robust if assembled properly. That's why there are so many of them still around even if built from kits.
That said, I feel grislybutter and kyguy are reasonable in their guidance. If the amp you have works well, installing new capacitors and maybe heavier gauge wire is about as far as you might care to go.
You don't say what you have for speakers, but if you have something on the more efficient side, Hafler could be a good match. The 220 was only adequate with my Rogers Studio 1 monitors at 86 dB. I replaced it with a Belles Model 1 that was a substantial improvement.
For financial perspective, there's a Belles 150 on eBay for $325. Good luck and happy listening on your journey!