The 9100's are very reliable. I did have one problem with both amps. A 1-meg resistor went bad in both amps(not at the same time about 2 months apart). They were about a year old when this happened. When I had them fixed the I was told that some time the manufacture could have gotten a bad run on that part. He found no reason for the breakdown other than the resistor was suspect.I once took out a grid resistor when replacing tubes. One of the KT90's was bad.I have not had a problem since then. I have owned them since 1998. They are played almost everyday for several hours. On the weekends 12 to 14 hours a day. As far as sound goes I love mine, but they are no longer stock.I have had some Musical Concepts mods done. In the stock form they are balanced with very good bottom almost like a SS amp. They are robust and have lots of headroom (THEY HAVE BALLS). The midrange is sweet and relaxed close to that of an EL-34. The upper end is very good extended but not too hot. I have to say this in the context that every system is different. What tubes you use are very important this includes the driver. I like KT-90's and use Mullards in the driver stage. When I bought these I was in transition from biamped Maggies(3a's). I was using 2 Musical Design D140's and a Nak Stassis7 for my subs. I also had the ARC V70 (nice amp),but not enough juice. I then heard the Aronovs driving the Von Schweikert Vr4 loved them and took them home for an audition, bought a pair. They sound a lot like the ARC M100's to me maybe a little more relaxed. Soon after I changed speakers to Merlin VSM. This the combo I still have and will for a long time. At the price I see the Aronovs going for it's a no brainer. Hope this helps you out. Feel free to email me if you have any more questions about the amps.
Sturgus
Sturgus