Y-Splitter question

[Jimmy the Greek]

I have an ASUS P8P67-Deluxe, and currently have my fans in the following configuration:

1. CPU_FAN - 120mm Scythe Kama Flex PWM
2. CHA_FAN1 - 120mm Nexus Real Silent
3. CHA_FAN2 - 120mm Nexus Real Silent
4. PWR_FAN1 - 120mm Noctua stock fan from NH-D14 (w/ ULNA)
5. PWR_FAN2 - 140mm Noctua stock fan from NH-D14 (w/ ULNA)

1, 2, and 3 all run at minimum speed until the CPU reaches a certain temperature.

4 and 5 are on the PWR_FAN headers and cannot be controlled by the motherboard. I'm running them with the Ultra Low Noise Adapters, because they're too loud at stock.

I don't really care about the noise during a high-performance task....I just want it to be silent when I'm browsing. The problem is, the Noctuas are both used to cool the CPU, and don't move enough air with the ULNAs. Ideally, I would move to this setup:

1. CPU_FAN - 120mm Scythe Kama Flex PWM
2a. CHA_FAN1 - 120mm Nexus Real Silent
2b. CHA_FAN1 - 120mm Nexus Real Silent
3a. CHA_FAN2 - 120mm Noctua stock fan from NH-D14
3b. CHA_FAN2 - 140mm Noctua stock fan from NH-D14

I would use a Y-Splitter for each of the chassis fan headers. Hopefully, this would let me run the Noctuas at full-tilt when necessary, but keep them quiet for the most part.

Do you see any issues with this, and controlling the temps of two different-model fans (120mm and 140mm Noctuas) from a single header?