I have an ISA One preamp.  I see there is a "digital" option for this.  What does the digital really add? (other than $$).

The ISA One digital option gives you a stereo AD channel.  You get another line in added to the preamp signal.
 
The quality is supposed to be good, in fact, excellence, since it was a "pro" unit.  Of course, it is 10 year old technology, so I would think something modern would be better, or as good.  However, there is a thread today on Gearslutz (I've seen you there) about that exact subject, and one user claims it is superior to his RME AD.

I saw the thread on gearslutz and what made me think about it and post the question.  I didn't understand what was really going on in that thread as it seems they were talking about interfacing the ISA One digital with a specific device.
 
Do I "need" an A/D converter like this?
 

Hi,
I have an ISA 428 (four preamp unit) and purchased the digital board so I am not sure about the single channel ISA one. One advantage of the 428 digital board is that it can also be dropped into the 8 channel ISA 828 should you ever go in that direction and need the digital IO. The board also has Wordclock I/O.
 
Depending on the unit you have, it will allow you to have from 44.1 kHz to 176.4 kHz ADAT IO. The manual shows how to set jumpers to select the options and channel combinations.
 
I have only needed 44.1 kHz so I left my board as factory default.
 
Soundwise??? very clean and dependable in a nutshell.
 
I took a look at the Focusrite site and the board for the ISA One and it looks different than the one for the 428/828 so I assume that it is a single channel I/O with Wordclock.
 
Hope that helps!
 
h

I'm going to pass on the digital card.  Looks more like I don't "need" it.  The ISA one analog works fine, it will even work good with a ribbon mic.
 

There are a lot of reviews out there on the difference between the ISA One and the stock pre amps on the Focusrite scarlett models. You might be intrigued by what some are saying. I was going to buy an ISA One but decided to put that money elsewhere (Joe meek 3EQ) and saved a bunch. I had contemplated the Universal audio Solo 610 but it was expensive compared to the used ISA One which were in the 300 range.