New to Digital

I absolutely love the Yamaha amp, so for now, I think the Chromecast Audio makes the most sense for the money.
I’ve  been an ADS fan since the late 70’s in college, and although mine still sound great to my ear, I also realize speakers have come a long way.
Thank you again for the suggestions!

+1 willemj, I concur with everything you wrote.

In my opinion, DAC's and streaming music are in an early stage. They will evolve quickly, so investing in the 'best' now will be an effort in futility.
For me, buying a DAC that the manufacturer can provide updates is an important factor. 
That being said, companies like Ayre (Codex) and Schiit (Gungnir and Yggy) offer a great product at a very reasonable price. 
If you want to stream to different rooms, the Bluesound Node is a great cost effective choice-And, you can output to a better quality DAC, too(though the internal DAC is pretty darn good, considering the price).
B

+1 willemj! It is always good to make up your mind without actually hearing something yourself.

Dave

If you have really old speakers you should probably start with replacing them. Some people puts most of their stereo budget in speakers and if you follow this you could look for speakers from $400 up to around $1000.
If you want to upgrade you digital part I have two ideas. You could get the Audioquest Beetle and a Chromecast. That's about $250 and should improve the sound. Or you could sell your amp and get a PS Audio Sprout, it has everything except speakers. If you like to tinker you could build a Raspberry Pi with a soundcard or spdif outputs and connect to your amp.

There is really no point in worrying about the quality of the Yamaha. See here for a test of the earlier AS700, identical but for the lack of digital inputs: http://www.avhub.com.au/product-reviews/hi-fi/yamaha-a-s700-integrated-amplifier-review-and-test-pag...
The results are seriously better than for many audiophile amplifiers costing perhaps ten times more. Its only limitation is the power output at around 2x100 watt rms. If you are using inefficient speakers in a larger room you may want more power. If not, you will be perfectly fine. Since the digital output of the Chromecast Audio has been shown to be bitperfect, there is no issue there either. I have not found any test yet of the Yamaha's internal DAC, but I would not expect anything other than excellent results.
So the only way in which you may be able to improve the sound of your system, is by getting really good modern speakers like the Harbeth M30.1. The rest of your system would be an excellent match even for such expensive speakers. But speaker choice does depend on personal preference, room size and music selection.