You can improve latency even further in jbridge by unticking "getaudiotime hack" and ticking "performance mode" in settings.
You don't have to do both, they are independant, but both effect latency and I do both with no negative effect so far, but I don't have Jamstix.
From London UK, working with a PC
Intel i7 2600K at 3.8 Ghz HT on,Thermalright VenomousXRT with Gigabyte GA-Z68x-UD5-B3,Corsair Force 3 SSD 120Gb, Samsung Spinpoint F3 1Tb Hdd, 16Gb Corsair Vengence PC12800 9-9-9-24,XFX Radeon 6450 HD passive,Corsair HX620W power, Samsung SATA DVD Drive and a SATA DVDRW Drive all in an Antec Solo case
Windows 7 64 bit ; TC Electronic Konnekt 24D, Alpha Track and M Audio axiom 49 ----
Cubase 6.0.5 with Amplitube 3.02, SampleTank 2.54, TRacks3 deluxe 3.1.2, CSR, SVX, Fabrik C and R, Kontact player + Slate Drums and loads of other plugs.