Things to know:
For many Ir protocols, the data is confined to 8 bits, and that is the case with the NEC1 protocol. It only takes 3 digits to represent 8 bits, and actually the nubers from 0 to 255. If you enter 256, it rolls over and is the same as entering 001. So 884 (Power) is the same as 116.

Next, there is a Lookup Tool.  If you select TV and device 0435, you can see the EFCs.  Button 5 (which provides the function of Power) is EFC 116.  The good news is that testing 884 (same as 116)  gave the same result as the 5 key.  The bad news is that apparently testing 116 didn't operate Power, which means something went awry during the testing.

The NEC protocol device number is 8 bits, and in the protocol is followed by its complement (255-device).  Similarly, it takes 8 bits of data, which is followed by the complement of the data.  So the LIRC data looks reasonable:
predata is 0xFF, the same as 0x00FF, which means device 0.  Looking at Power, we see the data is 0xB24D. B2 + 4D is FF, so the function data for Power is 0xB2 (178 decimal).

I've used RemoteMaster to convert between EFCs and function numbers.  WIth the NEC protocol, it usually makes sense to list function numbers which are the bit reversed complement of the data like B2 above.  So in the following table, I've listed EFC, OBC (which is the conventional function number, and the hex numbers from the LIRC table.  All of the OBC above 127 are generated using the LIRC data, and the ones below 127 arise from the behavior of the remote using 0435 or the results of your tests.  It turns out that all of the LIRC numbers are even (like B2) and all of the discovered numbers are odd.  In fact, with 2 exceptions, for the same function, the LIRC numbers are complements of the discovered numbers.  This is somewhat unusual, but it appears that the Vistron is responding to either the first or second byte of the data in the NEC protocol.   Here I've made the assumption that when you've referred to e.g. "7", it is really preset 7.

So I recommend that you use the OBCs above 127, and use the 994 keymove commands to store the corresponding EFCs to the buttons of your choice.  Use these instructions if you aren't familiar with keymoves.

mode
18
255
0
 
preset 3
14
254
80
 
preset 2
12
252
                             C0
 
play
19
251
20
 
stop
15
250
                            A0
 
reply
17
249
60
 
preset 4
142
246
90
 
skip prev
144
245
50
 
RC_up
145
241
70
 
preset 1
82
239
8
 
preset 9
78
238
88
 
back
80
237
48
 
recall
81
233
68
 
preset 0
77
232
                            E8
 
preset 7
206
230
98
 
RC_dpwn
208
229
58
 
preset 8
204
228
                            D8
 
browse
211
227
38
 
preset 5
207
226
                            B8
 
skip next
209
225
78
 
preset 6
205
224
                            F8
 
--/-
34
191
2
 
vol down
162
183
12
 
vol up
163
179
32
 
Power
159
178
                            B2
 
select
99
171
                            2A
 
test V +
36
76
                            CD
comp
test v-
37
72
                        ED         
comp
test -/--
165
64
                            FD
comp
test Media Player (mode)
246
30
87
?? comp to back
test preset 5
248
29
47
comp
rem PR+ (Ch+) fun 8
251
27
27
preset 8? comp
rem PR- (CH-) fun down
247
26
                         A7
comp
test preset 7
249
25
67
comp
rem 0 fun 7
249
25
67
preset 7? comp
rem 8 fun 0
122
23
17
preset 0 comp
rem 7 fun recall preset
118
22
97
?? comp to skip next
rem 5 fun Power
116
20
                 D7
comp to r1c3 (not present)
rem 3 fun back
119
18
                  B7
comp
rem 2 fun pr 9
121
17
77
preset 9? comp
rem 1 fun 1
117
16
                  F7
preset 1? comp
testv-(2)
58
15
                  0F
no match
test up
54
14
                  8F
comp
test preset 4
57
9
                  6F
comp
test preset 2
187
3
                  3F
comp
rem mute fun 2
187
3
             3F                
preset 2? comp
test preset 3
185
1
                  7F
comp