Owning the MoXF, I can say that the MoXF and Motif XF are only able to compete with the Integra in this symphonic department if you expand it with orchestral libraries for the flash board. I did so, bought 2 libraries, and still to my ears the MoXF is about on a par with the Integra.
I'm quite sure the on-board sounds of the Tyros do not include such specialized, differentiated orchestral string samples as the Roland SRX 04 Symphonic Strings expansion (dedicated violin, viola, celli and basses sections, big and small etc.), similarly regarding the SRX 10 Brass.
Now, these libraries I bought for the MoXF (e.g. Garritan Personal Orchestra Lite for Motif XF) - I just found they are obviously NOT compatible to the Tyros flash board (which is no wonder as the MoXF and Motif use a voice architecture composed of waveform elements). Can you only use the Tyros flash board for Yamaha's own voice expansions? These include a lot of solo instruments like saxophones, celtic etc., but obviously not special symphonic sounds.