Adding data from multiple Excel files to two lists
Your problem is not with 5 (or more) loops. Your problem is that you mixing code of different nature: walking over filesystem and name matching, and processing of files into single chunk of code. 

Separate it into different functions calling each other:

def process_worksheet(wb, worksheet_name):
    sheet = wb.sheet_by_name(worksheet_name)
    # ...

def process_xslx(path):
    wb = xlrd.open_workbook(path)
    worksheets = wb.sheet_names()
    for worksheet_name in worksheets:
        if worksheet_name.rfind('7600') != -1 :
            process_worksheet(wb, worksheet_name)

for root,dirs,files in os.walk(src):
    files = [ _ for _ in files if _.endswith('.xlsx') ]
    for file in files:
        process_xslx(os.path.join(root, file))


Another option is to use generators to hide some details on how iteration is performed. For example, instead of walking over filesystem, let generator yield workbooks:

def walk_xlsx(src):
    for root,dirs,files in os.walk(src):
        files = [ _ for _ in files if _.endswith('.xlsx') ]
        for file in files:
            wb = xlrd.open_workbook(os.path.join(root, file))
            yield wb

for wb in walk_xlsx(src):
    # filter() is also a generator which yields only 
    # worksheet names that have '7600' in their names 
    worksheets = filter(lambda wn: '7600' in wn, wb.sheet_names())
    for worksheet_name in worksheets:
        # ...