I believe the HK AP2500 is a clean, musical pre-amp. After listening through several speakers and amps over the past four years (Monitor Audio, Martin Logan, Counterpoint, Arcam), it has brought me quite a bit of pleasure in both detail and pace. No additives! Yet, extremely lively. I bought it used, so I never did find much information on the AP Signature Series line. If any one has any information, please...! I would highly recommend (if you manage to find one) this signature series pre-amp as an introduction to separates. A great bargin!