Thiel CS1.2 vs. Ohm Walsh 2

I’ve had Thiel speakers in my main rig since 1996. First with the CS .5, which is a little smaller than the 1.2, and since 2011 the CS 2.4 which is a decent bit larger. They are fabulous speakers. I also happen to have B&W 684 speakers fronting my home theater setup. The Ohm speakers I cannot speak to. My only concern would be is if your Denon AV receiver would be up to the task. Thiel speakers are demanding speakers when it comes to amplification. You really need a decent high current stereo amp to handle the nominal 4 ohm load which may well dip below 4 ohms at times. I have my doubts about the Denon AV receiver being a good match.

Concerning power requirements.   Need high current amp that is easily 4 ohm stable.   Your B&W 685 speakers are 8 ohm speakers with 88 db sensitivity.   The CS 1.2 are rated at 4 ohm and 87 db.  4 ohm is a much more demanding load than 8 ohm.   At minimum you need 40 watts per channel rms with both channels being driven at the same time with something considerably less than 1% THD 20-20Khz; and I'd be looking for something more.
Suitable amplification will likely cost more than the speakers are currently going for.

If you don't have suitable power and the speaker requires it you can literally fry the speaker.   

Yes, NAD, especially their Class A/B amps, would likely make for a more suitable match.

And if a manufacturer does not specify a 4 ohm spec the amp is likely not stable down to 4 ohms.

So are you looking for a power amp or an integrated amp?
(A basic power amp would require another component to perform the preamp chores)

And very importantly, what is your budget?

To use the Denon as a preamp you need a stereo variable line out.  If the line out is fixed .... it won't do. If it has a stereo pre out ... that would be best.

If the Denon is not 4 ohm stable, then the risk would be to the speakers.
When speakers ask for more power than the amp can safely deliver, then the amp clips, and speaker components overheat, literally frying the speaker and potentially damaging speaker components.

If you can stretch your budget to $399 ... then my suggestion would be to look at the Emotiva TA-100 in their BASX line.  You could buy that directly brand new from Emotiva ... and that should match up well with the Thiel CS 1.2 speakers.   And that is well suited to being used as a starter pre amp down the road.