http://www.tssupport.com/multicharts/datafeeds/
DTN is my recommendation, I think it gives the best price/performance combination.
(Note that the information on TSS site is out of date there is now 30 days of tick history)
However good the software, it is impossible to cater for the incompetence of every user. TSS support is some of the best I have ever encountered. It is such a shame that you didn't bother contacting them before posting here.
Because MultiCharts supports a large number of datafeeds and they all have different formats so you need to set the symbols up and supply the information. It's not really that complicated and if you are still struggling contact TSSupport via on-line chat when they are open next week and they'll...
Yes MultiCharts is multi threaded, so upgrading to a quad core isn't going to help. Anyway as someone already pointed out that is more about calculating indicators.
One thing to look at is right click on the DTN icon in the system tray > Support > Launch Diagnostics. Enter a test symbol click...
I usually monitor about 40 symbols using DTN IQfeed and MultiCharts and don't experience any lag compared to my IB feed on another PC. MultiCharts does use about 30-40% of my quad core processor when the market is fast. Does IRT multi thread using both cores? I think it's probably an IRT/IQ...
It was an IB problem, I contacted support and the only response I got was. "We are aware of this problem"
Shame they didn't update the system status until it had been down for half an hour.