I got a SLO and a X99 preamp. Either you love the Soldano voicing or you don't. Some people hate it. Some people love it. I'm in the second category.
The SLO is awesome IMHO. Perfect amp for me. Great lead channel of course but the crunch channel is marvellous as well. Really works well with boost pedals, cleans up very well with volume knob, great chimy gritty clean when gain set low. I keep hearing it's a one trick pony to play high gain lead only but I totally disagree with that opinion. It's super versatile. You can play any style of music with it, from funk to country, to classic rock to death-metal. It always cuts thru the mix with authority and sounds great no matter what.
It's not perfect in stock form though. The loop kinda sucks. Have it modified by a good tech to move it after the tone stack (my local guy did it for $100) and you're good to go.
The X99 is the greatest preamp ever made IMHO. Super reliable, awesome sound and a myriad of different tones in there. I have mine plugged in the loop return of the SLO. It works great. It's been several years I have no GAS for any amp. I wouldn't spit on a real 60s Vox AC30TB or an original 68 plexi of course but nothing else really gets me going...