So I got a new computer a few months back... a custom audio/video system from ADK and a huge improvement over my last one in terms of the memory and specs and all that.  (Intel Core i7 4770, 3.4 GHz, 16 GB RAM)  But for some reason I can't use the input monitoring on this system, because as soon as I hit record there's a bad echo on the effect signal.  (Note that it sounds okay before RECORD is going.) 
 
Even on my much crappier PC of old, I could get this to work right so I could hear the effect signal while recording, so I'm wondering what the issue is here... by all rights, it should work much smoother now, right?  Does it maybe have something to do with using a USB capture device now (Roland Duo Capture EX) as opposed to an in-board soundcard (Echo Mia) previously? 

When I run the Wave Profiler it shows the following: Buffers in Playback Queue = 2, Buffer size/effective latency = 18 msec (792 samples).

Any ideas what would help with that?
 
Thanks!

The good news is that it's not a problem with your new computer.
That buffer is way too big, and you will hear an echo at an effective latency of 18ms.
Total roundtrip is probably 30-40ms.
Be sure you are using the most current drivers from Roland. The ones that came with the Duo-Capture are most likely not current.
Try using the ASIO drivers. You are probably using WDM if the Wave Profiler runs. open the ASIO panel and change your buffer to a smaller size. Usually 128 will be ok. You can try to go smaller, if the Duo will support it.
The Duo is a little slim on features. You might want to consider another unit if it is not effective at low latencies.

PCI cards are good for latency because they are more directly attached to you MoBo, USB will always add some latency. The Roland interfaces are not the best performers for RTL. Jim Roseberry posted a list of interfaces with their performance specs here once and I should have bookmarked it as it was very revealing. 
 
Anyhow, RTL has little to do with how much horsepower a computer has , it's in the drivers. 
Worth noting, is some efxs add a lot more latency that others. Example, I can use the Sonitus EQ or compressor while tracking but not the LP64 type, They add a lot of latency as they are "look ahead" efxs. My practice is to bypass all bins while recording ( tracking) this way I'm guaranteed my best syncing of tracks. 
 

If you're describing an actual echo (double sounds) rather than a delay, it's because you're monitoring directly as well as through the computer. Turn input echo off and use your interface's direct monitoring, or if you need to hear the effects, turn the zero-latency monitor effect off on the interface. As noted above, you'll also need to lower your latency or it'll be uncomfortable playing with a long delay.