In this case it was just experience as I tried the exact same test. IMO, a simple rack mount compressor inserted between the pre and power amp works best to raise gain plus you have compression if yo need it. It's already a rack mount set up so no big issue with convenience. The downside is being mindful of the compressor output control. As far as sound quality or S/N goes, my dbx 160 and Behringer MDX1400 work perfectly for this application and are both inexpensive and liquid on the used market.