Ton Hankins makes a good point. Personally, I've always felt that the preamp is more important to get right than the amp. That's why I asked about the "power" issue as a matter of actual power or power in terms of sound quality. Given that your current amp should have more than enough power, epically with the JM Labs being very efficient, I take it you mean the latter of the 2 types.
With regards to picking an amp, I've owned a dna250 and have listened to the BAT on many ocassions, but never owned one. They are both excellent and if I were to pick just from these 2 I would get the BAT. If you have listened to both, and like the dna250 better, I would recommend something different. I felt the dna's biggest strength was in the midrange. It was very pure, clean and detailed. I thought the highs and lows were just OK but not great. In your used price range, you should be able to pick up an Ayre V5 used. This is what I currently use. Sound wise, it picks up where the dna leaves off and takes everything to a different level. It improves on the excellent mids of the dna but also brings the frequency extremes to the same level of quality of the mids. For me, its an amazing amp. For you, I would definately encourage you to listen to it first. Don't buy it just because I like it, you have to like it.
Since you mentioned the BAT, I thought of another approach you may like. BAT makes a great integrated that combines a solid state amp with your choice of a solid state preamp or 2 different tube preamps. They also offer a phono stage as well. You save money by putting 3 components in 1 box, don't have to deal with all the cables and have the piece of mind that all 3 things will work well together. You will even have the option of using another source such as a CD player, that you don't have now with your current system.