I remember seeing somewhere that I can't simultaneously use asc0 and
   asc1 on a 3000/400, am I recalling this correctly?


these are the SCSI devices connected to my 3000/400:

sd0 at scsibus0 targ 0 lun 0: <DEC, RZ26     (C) DEC, T386> SCSI2 0/direct fixed
sd1 at scsibus0 targ 1 lun 0: <DEC, RZ25     (C) DEC, 0700> SCSI2 0/direct fixed
cd0 at scsibus0 targ 4 lun 0: <DEC, RRD42   (C) DEC, 4.5d> SCSI2 5/cdrom removable
st0 at scsibus1 targ 4 lun 0: <DEC, TLZ06     (C)DEC, 0389> SCSI2 1/sequential removable
sd2 at scsibus2 targ 0 lun 0: <COMPAQ, C2490A, 4188> SCSI2 0/direct fixed
sd3 at scsibus2 targ 1 lun 0: <COMPAQ, C2490A, 4188> SCSI2 0/direct fixed
sd4 at scsibus2 targ 2 lun 0: <COMPAQ, C2490A, 4188> SCSI2 0/direct fixed
sd8 at scsibus4 targ 2 lun 0: <SEAGATE, ST11200N SUN1.05, 9500> SCSI2 0/direct fixed
sd9 at scsibus4 targ 3 lun 0: <MICROP, 2112-15MQ1001901, HQ30> SCSI2 0/direct fixed
sd10 at scsibus5 targ 0 lun 0: <DEC, RZ28M    (C) DEC, 0568> SCSI2 0/direct fixed
sd11 at scsibus5 targ 1 lun 0: <DEC, RZ28     (C) DEC, D41C> SCSI2 0/direct fixed
sd12 at scsibus5 targ 5 lun 0: <DEC, RZ28M    (C) DEC, 0568> SCSI2 0/direct fixed


yes, it has 6 scsi busses. :-)  i've not experienced any problems with
accessing the tape drive while the disks.  i do recall hearing that it
was an *old* problem, fixed many years ago, though.