Well it turns out that sync'ing to -current as of today appears to have
fixed the problem.  ACPI and ISA attachments are both able to print just
fine with or without DMA turned on.  Not terribly useful for debugging, but
heck, it works and that's mostly what's important. :-)  

Below is the info for the ISA and ACPI attachments with verbose/debug/etc.
turned on, in case it's of any use in the future.

ISA attachment:
atppc0 at isa0 port 0x378-0x37f irq 7 drq 3: AT Parallel Port
atppc0: FIFO <depth,wthr,rthr>=<16,8,8>
atppc0: capabilities=3f<INTR,DMA,FIFO,PS2,ECP,EPP>
ppbus0 at atppc0
n2Tppbus0<1284>: error=3 status=0xd8 event=24
/NIBBLETn4Tppbus0<1284>: error=3 status=0xd8 event=24
/PS2Tn16Tppbus0<1284>: error=3 status=0xd8 event=24
/ECPTn16Tppbus0<1284>: error=3 status=0xd8 event=24
ppbus0<1284>: error=1 status=0xc8 event=7
TTppbus0<1284>: error=3 status=0xd8 event=24
n8Tppbus0<1284>: error=3 status=0xd8 event=24
ppbus0<1284>: error=1 status=0xc8 event=7
TTppbus0<1284>: error=3 status=0xd8 event=24

ppbus0: IEEE1284 device found.
ppbus0: Probing for PnP devices.
n2Tppbus0<1284>: error=3 status=0xd8 event=24
Tppbus0: <PnP> 78 characters: M(0x4d) F(0x46) G(0x47) :(0x3a) B(0x42)
r(0x72) o(
0x6f) t(0x74) h(0x68) e(0x65) r(0x72) ;(0x3b) C(0x43) M(0x4d) D(0x44)
:(0x3a) P(
0x50) J(0x4a) L(0x4c) ,(0x2c) P(0x50) C(0x43) L(0x4c) ,(0x2c) P(0x50)
C(0x43) L(
0x4c) X(0x58) L(0x4c) ,(0x2c) P(0x50) O(0x4f) S(0x53) T(0x54) S(0x53)
C(0x43) R(
0x52) I(0x49) P(0x50) T(0x54) ;(0x3b) M(0x4d) D(0x44) L(0x4c) :(0x3a)
H(0x48) L(
0x4c) -(0x2d) 1(0x31) 6(0x36) 5(0x35) 0(0x30) _(0x5f) 1(0x31) 6(0x36)
7(0x37) 0(
0x30) N(0x4e)  (0x20) s(0x73) e(0x65) r(0x72) i(0x69) e(0x65) s(0x73)
;(0x3b) C(
0x43) L(0x4c) S(0x53) :(0x3a) P(0x50) R(0x52) I(0x49) N(0x4e) T(0x54)
E(0x45) R(
0x52) ;(0x3b)
ppbus0: <Brother HL-1650_1670N series> PRINTER PJL,PCL,PCLXL,POSTSCRIPT
lpt0 at ppbus0: port mode = 1<COMPATIBLE>


ACPI attachment:
atppc0 at acpi0 (PNP0401): AT Parallel Port
atppc0: io 0x378-0x37f,0x778-0x77b irq 7 drq 3
atppc0: FIFO <depth,wthr,rthr>=<16,8,8>
atppc0: capabilities=3f<INTR,DMA,FIFO,PS2,ECP,EPP>
ppbus0 at atppc0
n2Tppbus0<1284>: error=3 status=0xd8 event=24
/NIBBLETn4Tppbus0<1284>: error=3 status=0xd8 event=24
/PS2Tn16Tppbus0<1284>: error=3 status=0xd8 event=24
/ECPTn16Tppbus0<1284>: error=3 status=0xd8 event=24
ppbus0<1284>: error=1 status=0xc8 event=7
TTppbus0<1284>: error=3 status=0xd8 event=24
n8Tppbus0<1284>: error=3 status=0xd8 event=24
ppbus0<1284>: error=1 status=0xc8 event=7
TTppbus0<1284>: error=3 status=0xd8 event=24

ppbus0: IEEE1284 device found.
ppbus0: Probing for PnP devices.
n2Tppbus0<1284>: error=3 status=0xd8 event=24
Tppbus0: <PnP> 78 characters: M(0x4d) F(0x46) G(0x47) :(0x3a) B(0x42)
r(0x72) o(
0x6f) t(0x74) h(0x68) e(0x65) r(0x72) ;(0x3b) C(0x43) M(0x4d) D(0x44)
:(0x3a) P(
0x50) J(0x4a) L(0x4c) ,(0x2c) P(0x50) C(0x43) L(0x4c) ,(0x2c) P(0x50)
C(0x43) L(
0x4c) X(0x58) L(0x4c) ,(0x2c) P(0x50) O(0x4f) S(0x53) T(0x54) S(0x53)
C(0x43) R(
0x52) I(0x49) P(0x50) T(0x54) ;(0x3b) M(0x4d) D(0x44) L(0x4c) :(0x3a)
H(0x48) L(
0x4c) -(0x2d) 1(0x31) 6(0x36) 5(0x35) 0(0x30) _(0x5f) 1(0x31) 6(0x36)
7(0x37) 0(
0x30) N(0x4e)  (0x20) s(0x73) e(0x65) r(0x72) i(0x69) e(0x65) s(0x73)
;(0x3b) C(
0x43) L(0x4c) S(0x53) :(0x3a) P(0x50) R(0x52) I(0x49) N(0x4e) T(0x54)
E(0x45) R(
0x52) ;(0x3b)
ppbus0: <Brother HL-1650_1670N series> PRINTER PJL,PCL,PCLXL,POSTSCRIPT
lpt0 at ppbus0: port mode = 1<COMPATIBLE>