You would need a separate instance of DSD for each digital feed. In my case, I have two separate feeds coming off of the same trunking system but one is digital and the other is analog so I only need one DSD instance running. The analog will come straight out of UT. As for computer requirements, I'm running a 2.1 gHz Dual-Core with 2.5 gb ram and running windows 8 x64. It has running: 3 rtl's, UniTrunker, DSD+, an audio level monitor, two of my own java apps, RadioFeed, and one instance of SDR# (for the moment). Also, usually a Chrome window open on my feed management page. I generally am only utilizing about 70-80% CPU load and 1.5-2 gb ram at any given time. Hopefully that gives you an idea of what you will need. Oh... it's also worth mentioning that I use a 4gb SD card with readyboost to aid in lightening some of the load and make page operations a little quicker. It won't always make a difference but when you are working with low ram (like I am) then it can make certain things faster. I'm also using just on onboard video which shares the primary ram so that doesn't help me either. In any case, that system runs my 3 rtl's and broadcasts my feed just fine.
As for my AlphaTags app, my intention is to release it to everyone fairly soon. I'm in the process of coding it to be relatively universal for the average user and am beta testing it with a few volunteers. I haven't had much free time in the past couple weeks but I plan to at least have a (mostly) stable beta version ready within the next week or two. If you like, send me an email so I can add your address to my mailing list, and I'll make sure to let you know when I have it available or if I happen to need another beta tester to help iron out any last bugs.
HuronPerthOPP@gmail.com. I also made another app to handle prioritization with my two feeds (digital and analog) to prevent them from stepping on each other but it's fairly customized to my specific setup. If you are familiar with coding in java, I suppose I could give you the source code for that and you could customize it to your needs. I call it AutoMute. I may be willing to make a releasable version of it but that will have to wait until I'm done with the AlphaTags app.