The floating point and extended registers are accessed thru the '!fpregs' command. This command depends on the cpu and the operating system, so floating point registers are usually stored in a quite weird way at kernel level.
Here's an example on intel with MMX and STX registers:
[0xB7F9E810]> !fpregs
cwd = 0x037f ; control swd = 0x0000 ; status
twd = 0x0000 ; tag fip = 0x0000 ; eip of fpu opcode
fcs = 0x0000 foo = 0x0000 ; stack
fos = 0x0000
mm0 = 0000 0000 0000 0000 st0 = 0 (0x00000000)
mm1 = 0000 0000 0000 0000 st1 = 0 (0x00000000)
mm2 = 0000 0000 0000 0000 st2 = 0 (0x00000000)
mm3 = 0000 0000 0000 0000 st3 = 0 (0x00000000)
mm4 = 0000 0000 0000 0000 st4 = 0 (0x00000000)
mm5 = 0000 0000 0000 0000 st5 = 0 (0x00000000)
mm6 = 0000 0000 0000 0000 st6 = 0 (0x00000000)
mm7 = 0000 0000 0000 0000 st7 = 0 (0x00000000)
And the same for mips:
[0x2AAA8820]> !fpregs
f00: 0xffffffffffffffff f02: 0xffffffffffffffff
f04: 0xffffffffffffffff f06: 0xffffffffffffffff
f08: 0xffffffffffffffff f10: 0xffffffffffffffff
f12: 0xffffffffffffffff f14: 0xffffffffffffffff
f16: 0xffffffffffffffff f18: 0xffffffffffffffff
f20: 0xffffffffffffffff f22: 0xffffffffffffffff
f24: 0xffffffffffffffff f26: 0xffffffffffffffff
f28: 0xffffffffffffffff f30: 0xffffffffffffffff
(On mips the default value for undefined registers is '-1' and not '0'.
You can enable them in the visual debugger view with the 'e dbg.fpregs=true' command. The '!fpregs*' command is also available to export the registers as flags.