I've had the Aronov LS-9601 integrated for about 5 years now and been very happy. Never had a single issue; the thing is a workhorse, puts out plenty of power with tube warmth, a full bottom and lots of detail. I threw some Golden Lion KT88's and 12AX7's in there to replace the Aronov stock tubes (which were fine as is) and it upped the sound a bit. I'm running them with a Benchmark DAC, Oppo BDP 93 and B+W Matrix 3 Series 2 speakers. I'm upgrading the speakers with Vandersteen 3A's this week, and looking forward to hearing them in the system. I haven't heard the Threshold 4000 so have no input for you there.