Due to the fact that solid state amps tend to have a lower input impedance, many tube preamps will not make the best bass into them, even though as transistors go, the Pass Labs amps are quite moderate.
The thing to look at is the output impedance of the preamp. Usually this is specified at 1KHz (1000 cycles per second). And usually that is a benign value. Where it counts is the output impedance at 20Hz. If its even spec'ced, you'll find it to be considerably higher.
If you want the bass to be right, there can't be any phase shift in the bass. To accomplish this, the preamp must go down to at least 2Hz. To this end, its really helpful if the output impedance be constant across the band rather than rising at lower frequencies (the ARC is slightly over double the 1KHz value at 20Hz, climbing considerably higher as frequency drops below this point). ARC specs 0.2Hz as its bottom cutoff, but does not say into what load. The higher the impedance of the load, the lower it can go. Its a good bet this value for the spec is 100KOhms or higher.
One thing to keep in mind- while the Pass Labs amps do support the balanced line standard, neither of the preamps you have in mind do, even though they are balanced. The balanced standard (AES48 which stands for 'Audio Engineering Society file 48')) is there for two reasons- to prevent ground loops and to prevent the interconnect cable from having an artifact. If you've ever auditioned and heard differences between audio cables then you know what I'm talking about.
To this end, the output of the preamp can't reference ground- instead the complete signal is set up so that the non-inverting output references its opposite and vice versa; ground is ignored and used only for shielding. Traditionally this was done with an output transformer when tubes were king and still is with solid state because of the grounding issue. Regardless there are tube preamps that support the standard.
The thing to look at is the output impedance of the preamp. Usually this is specified at 1KHz (1000 cycles per second). And usually that is a benign value. Where it counts is the output impedance at 20Hz. If its even spec'ced, you'll find it to be considerably higher.
If you want the bass to be right, there can't be any phase shift in the bass. To accomplish this, the preamp must go down to at least 2Hz. To this end, its really helpful if the output impedance be constant across the band rather than rising at lower frequencies (the ARC is slightly over double the 1KHz value at 20Hz, climbing considerably higher as frequency drops below this point). ARC specs 0.2Hz as its bottom cutoff, but does not say into what load. The higher the impedance of the load, the lower it can go. Its a good bet this value for the spec is 100KOhms or higher.
One thing to keep in mind- while the Pass Labs amps do support the balanced line standard, neither of the preamps you have in mind do, even though they are balanced. The balanced standard (AES48 which stands for 'Audio Engineering Society file 48')) is there for two reasons- to prevent ground loops and to prevent the interconnect cable from having an artifact. If you've ever auditioned and heard differences between audio cables then you know what I'm talking about.
To this end, the output of the preamp can't reference ground- instead the complete signal is set up so that the non-inverting output references its opposite and vice versa; ground is ignored and used only for shielding. Traditionally this was done with an output transformer when tubes were king and still is with solid state because of the grounding issue. Regardless there are tube preamps that support the standard.