What soundcard works/works best with Maverick?

Some time ago I bought a MacPro 2.8 Ghz Quad-Core Intel Xeon, with 8GB 1066 Mhz DD3. It runs 10.9.3, and I could update it to Yosemite, but I am not sure if I want to. Now, I have a Saffire Focusrite LE soundcard, and whan I used that with my MacPro G5 it worked perfectly fine, and I had no problems at all. Now, I connected the Saffire LE to my new MacPro, but not only for recording in Garageband (I got Logic also recently, but haven´t tried it yet), I connected it to my speakers from the rear of the soundcard, so I could get a good sound out. It worked fine at first.., only by choosing the Saffire in the audiosystem for audio options.. I have not tried connect the Saffire as an aggregate device yet, though.. But suddenly the Saffire start to disconnect from the computer, and there were no sound in the speakers. When I changed the firewire inputs, it started to work again. Because of this problem, I started to look on the internet what could have been the reason for the problem. I then find, that there seem to be many problems along the way, with several different soundcards, especially running with Maverick.. I tried to update the Saffire with my laptop, a Macbook 10.7.. but when it was just about to update, the screen went shady, and the computer crashed! I tried once more, but the same thing happened again, so I can´t update the Saffire either.. Now, I think i´s time to buy a new soundcard. I am not a professional, but I am not a beginner either, so I would like to buy something good working, but not too expensive. But still, what soundcard works with Maverick? Shall I update to Yosemite maybe? I looked at Pre Sonos Audiobox, but I couldn´t fins any with firewire. I looked at Saffire too, the Pro 14 or Pro 24..? Do someone have any clue what to do, that is best in this case? I am grateful for some advice..

Thank You! 😀