Yamaha makes two lines of home furniture cabinet digital pianos. One series is called the Clavinova CLP & CVP and the other is called the Arius series YDP (stands for Yamaha Digital Piano). Yamaha America allows only regular local piano stores to carry the Clavinova series and the YDP series is usually available at the full line music stores such as Guitar Center, Sam Ash, and many on-line internet stores. Sometimes a local piano store will carry both piano lines, but not often. The Clavinova prices are never advertised on the internet in the US because you have to find & purchase them in a local store, but the Arius YDP piano prices are advertised locally and on the internet and the YDP's are always advertised everywhere at generally the same discount price.
The CLP320 and YDP161 also share the same piano tone called Pure CF sampling. This piano sound is taken from Yamaha's acoustic CF series piano. This difference is supposed to make the piano tone sound better than previous models. But as with all pianos, you have to know what to listen for and be experienced in piano tone to notice the difference.
Although the YDP161 and Clavinova CLP320 have the same cabinet design (with some minor differences), the 161 comes in just one color as opposed to the CLP320 which comes in a few different colors. That may be an important option depending on the furniture and design colors in your home although since the CLP320 is discontinued now, it is a mute point. As far as these pianos go, it's the touch, piano tone, and pedal system that make them a good choice over some of the competitors. The other features and sounds (10 instrument sounds on the YDP161) on both pianos are very basic and offer nothing special (in my opinion). And I don't care much for the panel layout at this price point because there are very few control access buttons but the YDP181 for $1699 does have a much better panel layout and would be a better choice for ease of use and also has very nice upgraded features. But if you need to keep the price down, then the YDP161 will be fine. However, neither piano has a USB/MIDI output to computer (only a regular MIDI output) which should be a standard item on these pianos especially at this price. I suspect there may be new Arius models next year which should take care of that issue among other things. The music education software for computers these days is very exciting and and Apple iPad is one of the best ways to utilize it connected to a digital piano so having a high speed core MIDI USB connection is important in my opinion.
Also, you should consider the Casio AP620 Celviano digital piano (pictured left) for an internet price of $1399. The AP620 piano tone & touch are (in my opinion) exceptional in this price range with Casio's 3-sensor dynamic response system producing a greater piano dynamic range and expression. it also has easier to use control panel functions with an LCD display screen. The Casio AP620 also has dedicated buttons, 250 instrument tones (as opposed to 10 on the Yamaha CLP161), 360 educational drum rhythms and full background accompaniment music (none on the Yamaha 161, CLP320 or on the new CLP430), an SD memory card slot with 4 banks of separate memory for storage and playback of General MIDI songs and lessons, ivory touch keys, front cabinet stabilization legs, and more. Hundreds of people throughout the US own the Casio AP620 piano and like it very much.
If you don't know about the Casio AP620, then you should check it out before you purchase a digital piano in this price range. I have written a blog review on the Casio AP620, so take a look when you have time.
Although the Yamaha YDP161 is a good digital piano choice, if you want to be in a lower price range, then I also recommend the Casio Celviano AP420 (left pic) with an internet price of just $1099. The AP420 is the direct competitor to the Yamaha YDP161 and has the ivory touch keys, USB to computer connection, 4-hand duet play function, an SD card memory storage for recording and playing songs, and a sturdier cabinet with height adjustable bench, all of which the Yamaha YDP161 does not have. The AP420 piano key touch and dynamics are identical to the Casio AP620 and better than the Yamaha, and the AP420 is $400 less than the Yamaha, so it really is a very good value and quite popular. I have played the Casio AP420 many times and am very impressed with it for its low price.