Look for an amp with at least 125 watts per side and doubles down into 4 ohms. This is why the BAT works so well - lots of power and unconcerned by drops in impedance.
Some other suggestions:
1. Musical Fidelity A5.5 Integrated amplifier or used A5
2. NAD M3 Dual Mono integrated amplifier or the new C375BEE - basically plain Jane version of the M3
3. Plinius 9100 or 9200 Integrated Amplifier
4. Naim Nait XS Integrated Amplifier - lower power compared to these others, but lots of apparent current on tap when needed - a musical over achiever (I think the Super Nait while more powerful is a bit over priced)
5. New Cambridge Audio Azur 840W amplifier paired with Cambridge's new 840E preamp, not an integrated but terrific sounding pair.
Some other suggestions:
1. Musical Fidelity A5.5 Integrated amplifier or used A5
2. NAD M3 Dual Mono integrated amplifier or the new C375BEE - basically plain Jane version of the M3
3. Plinius 9100 or 9200 Integrated Amplifier
4. Naim Nait XS Integrated Amplifier - lower power compared to these others, but lots of apparent current on tap when needed - a musical over achiever (I think the Super Nait while more powerful is a bit over priced)
5. New Cambridge Audio Azur 840W amplifier paired with Cambridge's new 840E preamp, not an integrated but terrific sounding pair.