All questions from a previous post has been answered since I bought Boston BA735 myself. well I will start from what is the difference between a analog speaker and a digital one? then go to signal and interface consecutively.
the speaker itself does not have things different because it's still plain speaker as we all know--you can still buy a bare speaker unit and change by yourself; however, what makes these two types distinct is the DAC inside the digital one while there is no any DAC in the analog speaker. In other words, the digital speaker will receive only digital signal which contains information of 0s and 1s, then translate that signal into analog by the DAC unit right before transmit to a speaker. This process differs to the analog one because normally a computer will transmit the signal to speakers directly by sound card which has the DAC built-in. You may think like I do why and what is the advantage of the digital speaker over the analog one. All can I say is almost none--in most cases--these days. It might have one significant advantage which is almost none CPU utilization because the CPU doesn't have to do anything about sound--just help transmitting throughout a digital port. The digital speaker will take care of the rest. Nonetheless, if you have such a great sound card like Sound Blaster Augidy or whatever so, you already have a very low CPU utilization and you will not take any advantages of your sound card at all by using the digital speaker. You may get the idea what it really is now, but this is the idea. I will show you about when using this what you have to do other than normal one.
The real problem of the digital speaker is you need a digital signal. You may think this is just simple because every single computer use digital to process anyway. Nevertheless, the default of sound output in every 
computer is analog. You may find hard to set it as a digital output. Most of modern sound cards have a digital output as a feature--not all of them though. For me, I find it very difficult to use this speaker. My on-board sound card doesn't have digital-output support, although its name is digital bla bla bla, so I have to use one of my spare SB Live! just to use this speaker. Believe it or not, I cannot work this out with my Linux box yet.
For a performance, I had Boston BA635 (analog) which is predecessor of BA735 before. I can't notice any different between two of them--maybe my ear is not that good though LOL.
For the connector, my misunderstanding is, for the digital output, it should be SPDIF or an optical port--the one I never ever have a chance to use. However, it's wrong. There are 2 types of digital connector--coaxial and optical. So it could be both optical and electrical signal that carry digital output. In my case--BA735, it use just plain cable. On one terminal is coax; another one is just mono headphone jack to connect with my PC-box. There is no significant differences between analog and digital at all. That should be the reason why only a few web sites mentioned this.
What you have to do to use this kind of speaker
You have to have a sound card that has digital output capability. The easiest way to know this is get yourself into Control Panel >> Sound and seek for "digital output only" feature in every single page. If you can find it, you're good to have a digital speaker. If you can't find any, go to manufacturer's web site and find its detail tech spec. You may get a good information.
Analog or digital speaker is just choice of preference. A performance is also on the same factor: price, model, and brand. All we have to do is understand what it really is and uses it efficiently.
