This is a bit of a scratchpad for me as I plug various things into the motherboard and see where they land in the groups.

There seems to be 8 IOMMU groups on this board. 

First run: RX480 in PCIe 3.0 slot, Audigy 2 in second PCI slot.

UPDATE: I was going to paste in multiple runs and show the differences in them, but spoilers, every PCIe and PCI slot in this thing other than the first PCIe3.0 16x is in Group 0… Which means the only way you can do any sort of GPU Passthrough is if your Linux video card is in the PCIe 2.0 slot, and you put your GPU to passthrough on the first PCIe3.0 slot. At least with the B350 chipset.

I was able to get the system to boot with my 5870 in the PCIe2.0 slot, so I may try swapping my video cards, blacklisting the 5870 in linux, then try to pass it through in the 3.0 slot.

Ungrouped.

00:00.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Device 1450
00:00.2 IOMMU: Advanced Micro Devices, Inc. [AMD] Device 1451

Group 0, Seems to be everything connected through the B350 Chipset.

00:01.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Device 1452
00:01.3 PCI bridge: Advanced Micro Devices, Inc. [AMD] Device 1453
# First Onboard USB controller
03:00.0 USB controller: Advanced Micro Devices, Inc. [AMD] Device 43bb (rev 02)
# First Onboard SATA controller Ports 1-4?
03:00.1 SATA controller: Advanced Micro Devices, Inc. [AMD] Device 43b7 (rev 02)
03:00.2 PCI bridge: Advanced Micro Devices, Inc. [AMD] Device 43b2 (rev 02)
1d:00.0 PCI bridge: Advanced Micro Devices, Inc. [AMD] Device 43b4 (rev 02)
1d:01.0 PCI bridge: Advanced Micro Devices, Inc. [AMD] Device 43b4 (rev 02)
1d:04.0 PCI bridge: Advanced Micro Devices, Inc. [AMD] Device 43b4 (rev 02)    
# Onboard ethernet controller.
1e:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 15)
1f:00.0 PCI bridge: ASMedia Technology Inc. ASM1083/1085 PCIe to PCI Bridge (rev 04)
# Second PCI Slot
20:01.0 Multimedia audio controller: Creative Labs EMU10k2/CA0100/CA0102/CA10200 [Sound Blaster Audigy Series] (rev 04)
20:01.1 Input device controller: Creative Labs SB Audigy Game Port (rev 04)
20:01.2 FireWire (IEEE 1394): Creative Labs SB Audigy FireWire Port (rev 04)

Group 1

00:02.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Device 1452

Group 2

00:03.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Device 1452
00:03.1 PCI bridge: Advanced Micro Devices, Inc. [AMD] Device 1453
# Top PCIe 3.0 16x slot.
22:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Ellesmere [Radeon RX 470/480] (rev c7)
22:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Device aaf0

Group 3

00:04.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Device 1452

Group 4

00:07.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Device 1452
00:07.1 PCI bridge: Advanced Micro Devices, Inc. [AMD] Device 1454
23:00.0 Non-Essential Instrumentation [1300]: Advanced Micro Devices, Inc. [AMD] Device 145a
23:00.2 Encryption controller: Advanced Micro Devices, Inc. [AMD] Device 1456
# Second USB controller
23:00.3 USB controller: Advanced Micro Devices, Inc. [AMD] Device 145c

Group 5

00:08.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Device 1452
00:08.1 PCI bridge: Advanced Micro Devices, Inc. [AMD] Device 1454
24:00.0 Non-Essential Instrumentation [1300]: Advanced Micro Devices, Inc. [AMD] Device 1455
# Second SATA controller. Ports 5 and 6?
24:00.2 SATA controller: Advanced Micro Devices, Inc. [AMD] FCH SATA Controller [AHCI mode] (rev 51)
# Onboard Audio
24:00.3 Audio device: Advanced Micro Devices, Inc. [AMD] Device 1457

Group 6

00:14.0 SMBus: Advanced Micro Devices, Inc. [AMD] FCH SMBus Controller (rev 59)
00:14.3 ISA bridge: Advanced Micro Devices, Inc. [AMD] FCH LPC Bridge (rev 51)

Group 7

00:18.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Device 1460
00:18.1 Host bridge: Advanced Micro Devices, Inc. [AMD] Device 1461
00:18.2 Host bridge: Advanced Micro Devices, Inc. [AMD] Device 1462
00:18.3 Host bridge: Advanced Micro Devices, Inc. [AMD] Device 1463
00:18.4 Host bridge: Advanced Micro Devices, Inc. [AMD] Device 1464
00:18.5 Host bridge: Advanced Micro Devices, Inc. [AMD] Device 1465
00:18.6 Host bridge: Advanced Micro Devices, Inc. [AMD] Device 1466
00:18.7 Host bridge: Advanced Micro Devices, Inc. [AMD] Device 1467