Question/Help Needed: Boomer who is totally inexperienced with DACs and streamers.

Since your Alexa device has a digital out  then you should be able to connect directly to the built in DAC of the NAD. From the link you sent, it looks like the DAC accepts USB in. If it does not have COAX in, then you may need to convert COAX to USB to get going. That would be a quick start to hear how the new amp sounds.  From there you can upgrade to a better dedicated streamer if and when you are ready. Dedicated streamers will sound better. But they use different software to control the music, which will take some getting used to. Tablets are usually better than from your phone. BlueSound is a logical step up and you can spend more on a streamer than you have in you entire system. It never ends. The BluOS software is easy and intuitive. Innuos software is very good as well. IMO, the control software is important. If you are not too tech savvy, then the software can be the Achilles heel of streaming enjoyment. Streaming services like Amazon, Qobuz, Tidal are supported by the BluOS. Amazon music may be more difficult to stream with other devices.

It looks like the BlueSound has optical and USB outs...so would I connect one of them to the corresponding input in the amp/DAC?  I guess then I control what I play via a phone or tablet?  Thanks!!!