I've never heard a Simaudio Titan, but I have Proceed HPA 2 & 3 amps that I use daily. They are superb.
The HPA 2 and 3 were basically Levinson models. I spoke with a dealer some years ago as they were selling the 5 channel. He said those were superb sounding amps and it was really a shame they discontinued the Proceed line as it gave people a taste of the Levinson sound. Those and are heavy like tanks. The only thing you need to be aware of is service and age. You cannot service those amps at Harman. There is a place in Mass (forget the name) that is recommende to service the Proceed amps. I think it's near Dedham, Ma. And in terms of age, all those amps will be at least 10 years old at this point. I think the Proceed line was stopped sometime around 2003 or so.
Just double-check on that. I've previously owned both AMP2s and AMP3s. I blew out a channel on one of my AMP3s. The only place with the know-how was in Dedham, MA. The local shops that I looked at--even the former Proceed dealers--don't have the local know-how to repair them any longer.
I absolutely loved my Proceed Amps but I'm simply saying that because Proceed is no longer in business and because Harman doesn't service them either you just need to be aware of what your options are before you buy. That's all.
I also recall the place in Dedham, MA having the option for me to ship the unit to them. So it wasn't the sort of thing where you needed to make a whole pilgrimage just to get the unit serviced.
The Proceeds use mostly generic parts; and they can be repaired. Two more repair shops are Pyramid Audio Repair and the Service Bench.
At the price they sell for used you will not find a better value for power and sound quality. They literally double their power into 4 ohms. I have an HPA3 and will NEVER part with it.
Internetmin writes, "The local shops that I looked at--even the former Proceed dealers--don't have the local know-how to repair them any longer." That differs from my experience in Santa Barbara. My Amp 3 was repaired locally, and the shop commented on what a pleasure it was to work on such a well built amp. A Proceed preamp or processor may be a different matter, but amps are much simpler.