The St. Thomas strings bundled with EmuX are ok pero kulang in expressiveness, IMO. The VirtuosoX has the following tremolo strings: Hall Section Tremolo 1, 2, & 3, 16 Violins Legato & Tremolo Stereo, 16 Violins Legato & Tremolo Mono, 16 Violins Pizzicato and Tremolo, 5 Violins Tremolo, 5 Violins Tremolo Mono, 5 Violins Pizz/Trems, 15 Violas Legato/Trems, 15 Violas Tremolo Strereo, 15 Violas Tremolo Mono, 10 Celli Tremolo Stereo, 10 Celli Tremolo Mono, 5 Celli Legato/Tremolo, 4 Basses Tremolo, 6 & 4 Basses Leg/Trem, 3 & 4 Basses Leg/Trem, and Bass & Celli Trem.
There are also spiccato and marcato samples, as well as solo vibrato and pizzicato samples for a total of 512 presets. There is a downloadable mp3 of the VirtuosoX on the Emu site... makes me kinda GAS for their more expensive Symphonic Orchestra soundbank.
EDIT: You SHOULD hear their Modern Symphonic Orchestra set... incredible samples; could give GPO a run for it's money.